Linux: Remove rseq support

The kernel ABI is not finalized, and there are now various proposals
to change the size of struct rseq, which would make the glibc ABI
dependent on the version of the kernels used for building glibc.
This is of course not acceptable.

This reverts commit 48699da1 ("elf:
Support at least 32-byte alignment in static dlopen"), commit
8f4632de ("Linux: rseq registration
tests"), commit 6e29cb3f ("Linux: Use
rseq in sched_getcpu if available"), and commit
0c76fc3c ("Linux: Perform rseq
registration at C startup and thread creation"), resolving the conflicts
introduced by the ARC port and the TLS static surplus changes.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>