Cleanup pure statement warning

The `you may be omitting necessary parentheses` hint in the message was
added when we used to get method references that became lambdas in statement
positions. Now these are an error and never reach this warning.

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -2403,7 +2403,7 @@ class MemberWithSameNameAsStatic()(using Context)
 class PureExpressionInStatementPosition(stat: untpd.Tree, val exprOwner: Symbol)(using Context)
   extends Message(PureExpressionInStatementPositionID) {
   def kind = MessageKind.PotentialIssue
-  def msg(using Context) = "A pure expression does nothing in statement position; you may be omitting necessary parentheses"
+  def msg(using Context) = "A pure expression does nothing in statement position"
   def explain(using Context) =
     i"""The pure expression $stat doesn't have any side effect and its result is not assigned elsewhere.
         |It can be removed without changing the semantics of the program. This may indicate an error."""

compiler/test-resources/repl/nowarn.scala

@@ -27,7 +27,7 @@ scala> def f = { 1; 2 }
 -- [E129] Potential Issue Warning: ---------------------------------------------
 1 | def f = { 1; 2 }
   |           ^
-  |A pure expression does nothing in statement position; you may be omitting necessary parentheses
+  |           A pure expression does nothing in statement position
   |
   | longer explanation available when compiling with `-explain`
 def f: Int

tests/neg-macros/annot-suspend-cycle.check

@@ -1,7 +1,7 @@
 -- [E129] Potential Issue Warning: tests/neg-macros/annot-suspend-cycle/Macro.scala:7:4 --------------------------------
 7 |    new Foo
   |    ^^^^^^^
-  |    A pure expression does nothing in statement position; you may be omitting necessary parentheses
+  |    A pure expression does nothing in statement position
   |
   | longer explanation available when compiling with `-explain`
 Cyclic macro dependencies in tests/neg-macros/annot-suspend-cycle/Test.scala.

tests/neg/i18408a.check

@@ -13,6 +13,6 @@
 -- [E129] Potential Issue Warning: tests/neg/i18408a.scala:4:16 --------------------------------------------------------
 4 |def test2 = fa({42; ()})
   |                ^^
-  |                A pure expression does nothing in statement position; you may be omitting necessary parentheses
+  |                A pure expression does nothing in statement position
   |
   | longer explanation available when compiling with `-explain`

tests/neg/i18408b.check

@@ -13,6 +13,6 @@
 -- [E129] Potential Issue Warning: tests/neg/i18408b.scala:4:16 --------------------------------------------------------
 4 |def test2 = fa({42; ()})
   |                ^^
-  |                A pure expression does nothing in statement position; you may be omitting necessary parentheses
+  |                A pure expression does nothing in statement position
   |
   | longer explanation available when compiling with `-explain`

tests/neg/i18408c.check

@@ -13,6 +13,6 @@
 -- [E129] Potential Issue Warning: tests/neg/i18408c.scala:4:16 --------------------------------------------------------
 4 |def test2 = fa({42; ()})
   |                ^^
-  |                A pure expression does nothing in statement position; you may be omitting necessary parentheses
+  |                A pure expression does nothing in statement position
   |
   | longer explanation available when compiling with `-explain`

tests/neg/nowarn.check

@@ -32,7 +32,7 @@ Matching filters for @nowarn or -Wconf:
 -- [E129] Potential Issue Warning: tests/neg/nowarn.scala:15:11 --------------------------------------------------------
 15 |def t2 = { 1; 2 } // warning (the invalid nowarn doesn't silence anything)
    |           ^
-   |           A pure expression does nothing in statement position; you may be omitting necessary parentheses
+   |           A pure expression does nothing in statement position
    |
    | longer explanation available when compiling with `-explain`
 -- Warning: tests/neg/nowarn.scala:14:8 --------------------------------------------------------------------------------
@@ -43,7 +43,7 @@ Matching filters for @nowarn or -Wconf:
 -- [E129] Potential Issue Warning: tests/neg/nowarn.scala:18:12 --------------------------------------------------------
 18 |def t2a = { 1; 2 } // warning (invalid nowarn doesn't silence)
    |            ^
-   |            A pure expression does nothing in statement position; you may be omitting necessary parentheses
+   |            A pure expression does nothing in statement position
    |
    | longer explanation available when compiling with `-explain`
 -- Warning: tests/neg/nowarn.scala:17:8 --------------------------------------------------------------------------------