[ADT] Remove llvm::empty

Note that I deprecated llvm::empty on September 18, 2022 in commit
6b49f30.

Author: kazutakahirata

llvm/include/llvm/ADT/STLExtras.h

@@ -376,13 +376,6 @@ void adl_swap(T &&lhs, T &&rhs) noexcept(
   adl_detail::adl_swap(std::forward<T>(lhs), std::forward<T>(rhs));
 }
 
-/// Test whether \p RangeOrContainer is empty. Similar to C++17 std::empty.
-template <typename T>
-LLVM_DEPRECATED("Use x.empty() instead", "empty")
-constexpr bool empty(const T &RangeOrContainer) {
-  return adl_begin(RangeOrContainer) == adl_end(RangeOrContainer);
-}
-
 /// Returns true if the given container only contains a single element.
 template <typename ContainerTy> bool hasSingleElement(ContainerTy &&C) {
   auto B = std::begin(C), E = std::end(C);