Update MIR doc.

Author: cjgillot

compiler/rustc_middle/src/mir/syntax.rs

@@ -1112,10 +1112,6 @@ pub enum Rvalue<'tcx> {
     /// For addition, subtraction, and multiplication on integers the error condition is set when
     /// the infinite precision result would be unequal to the actual result.
     ///
-    /// For shift operations on integers the error condition is set when the value of right-hand
-    /// side is greater than or equal to the number of bits in the type of the left-hand side, or
-    /// when the value of right-hand side is negative.
-    ///
     /// Other combinations of types and operators are unsupported.
     CheckedBinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),