The x86_64 specific implemention has CFI directives like
`.cfi_adjust_cfa_offset 128` which are incorrect when RBP is used as the
canonical frame address.
This follows the spirit of the following two commits by removing the
x86_64 specific implementation. The generic implementation will be used.
* eb76e5b465a4b7b569cde4b4f57d1fcb4695c1c6 ("nptl: Reinstate pthread_timedjoin_np as a cancellation point (BZ#24215)")
* c50e1c263ec15e98da3235e663049156fd1afcfa ("x86: Remove arch-specific low level lock implementation")
15c4b8cbcc