[OpenCL] Remove spurious atomic_fetch tablegen builtins

The `int` and `long` versions of these builtins already provide the
necessary overloads for `intptr_t` and `uintptr_t` arguments, as
`ASTContext` defines `atomic_(u)intptr_t` in terms of the `int` or
`long` types.

Prior to this patch, calls to those builtins with particular argument
types resulted in call-is-ambiguous errors.

Differential Revision: https://reviews.llvm.org/D98520