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 48699da1c4 ("elf:
Support at least 32-byte alignment in static dlopen"), commit
8f4632deb3 ("Linux: rseq registration
tests"), commit 6e29cb3f61 ("Linux: Use
rseq in sched_getcpu if available"), and commit
0c76fc3c2b ("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>

nptl/pthread_create.c

@@ -33,7 +33,6 @@
 #include <default-sched.h>
 #include <futex-internal.h>
 #include <tls-setup.h>
-#include <rseq-internal.h>
 #include "libioP.h"
 #include <sys/single_threaded.h>
 
@@ -386,9 +385,6 @@ START_THREAD_DEFN
   /* Initialize pointers to locale data.  */
   __ctype_init ();
 
-  /* Register rseq TLS to the kernel.  */
-  rseq_register_current_thread ();
-
 #ifndef __ASSUME_SET_ROBUST_LIST
   if (__set_robust_list_avail >= 0)
 #endif
@@ -585,15 +581,6 @@ START_THREAD_DEFN
      process is really dead since 'clone' got passed the CLONE_CHILD_CLEARTID
      flag.  The 'tid' field in the TCB will be set to zero.
 
-     rseq TLS is still registered at this point.  Rely on implicit
-     unregistration performed by the kernel on thread teardown.  This is not a
-     problem because the rseq TLS lives on the stack, and the stack outlives
-     the thread.  If TCB allocation is ever changed, additional steps may be
-     required, such as performing explicit rseq unregistration before
-     reclaiming the rseq TLS area memory.  It is NOT sufficient to block
-     signals because the kernel may write to the rseq area even without
-     signals.
-
      The exit code is zero since in case all threads exit by calling
      'pthread_exit' the exit status must be 0 (zero).  */
   __exit_thread ();