Simplify hasPrecisePrefix check

`NoPrefix.isStable` already returns true.

Author: smarter

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -290,7 +290,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
            *  See pos/i17064.scala for a test case
            */
           def hasPrecisePrefix(tp: NamedType) =
-            tp.prefix.isStable || tp.prefix == NoPrefix
+            tp.prefix.isStable
 
           info2 match
             case info2: TypeAlias =>