[TargetLowering] Update the description of getShiftAmountTy. NFC

After f4d058f, the LegalTypes
argument is no longer used.

Author: topperc

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -400,12 +400,10 @@ class TargetLoweringBase {
   virtual MVT getScalarShiftAmountTy(const DataLayout &, EVT) const;
 
   /// Returns the type for the shift amount of a shift opcode. For vectors,
-  /// returns the input type. For scalars, behavior depends on \p LegalTypes. If
-  /// \p LegalTypes is true, calls getScalarShiftAmountTy, otherwise uses
-  /// pointer type. If getScalarShiftAmountTy or pointer type cannot represent
-  /// all possible shift amounts, returns MVT::i32. In general, \p LegalTypes
-  /// should be set to true for calls during type legalization and after type
-  /// legalization has been completed.
+  /// returns the input type. For scalars, calls getScalarShiftAmountTy.
+  /// If getScalarShiftAmountTy type cannot represent all possible shift
+  /// amounts, returns MVT::i32.
+  /// \p LegalTypes is no longer used and will be removed from the interface.
   EVT getShiftAmountTy(EVT LHSTy, const DataLayout &DL,
                        bool LegalTypes = true) const;