[NFC] Remove deprecated Argument::getParamAlignment() declaration (#169911)

The implementation of Argument::getParamAlignment() was removed in
commit b55f83d, but the declaration in
Argument.h was left behind. Remove it.

NFC.

Author: melver

llvm/include/llvm/IR/Argument.h

@@ -108,12 +108,6 @@ class Argument final : public Value {
   /// returned. Otherwise, nullptr.
   LLVM_ABI Type *getPointeeInMemoryValueType() const;
 
-  /// If this is a byval or inalloca argument, return its alignment.
-  /// FIXME: Remove this function once transition to Align is over.
-  /// Use getParamAlign() instead.
-  LLVM_ABI LLVM_DEPRECATED("Use getParamAlign() instead",
-                           "getParamAlign") uint64_t getParamAlignment() const;
-
   /// If this is a byval or inalloca argument, return its alignment.
   LLVM_ABI MaybeAlign getParamAlign() const;