AArch64: Remove Falkor memcpy

The latest implementations of memcpy are actually faster than the Falkor
implementations [1], so remove the falkor/phecda ifuncs for memcpy and
the now unused IS_FALKOR/IS_PHECDA defines.

[1] https://sourceware.org/pipermail/libc-alpha/2022-December/144227.html



Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
(cherry picked from commit 2f5524cc)