elf: Disable most of TLS modid gaps processing [BZ #27135]

Revert "elf: Fix DTV gap reuse logic [BZ #27135]"

This reverts commit 572bd547d5.

It turns out that the _dl_next_tls_modid in _dl_map_object_from_fd keeps
returning the same modid over and over again if there is a gap and
more than TLS-using module is loaded in one dlopen call.  This corrupts
TLS data structures.  The bug is still present after a revert, but
empirically it is much more difficult to trigger (because it involves a
dlopen failure).

elf/dl-tls.c

@@ -191,7 +191,10 @@ _dl_next_tls_modid (void)
 size_t
 _dl_count_modids (void)
 {
-  /* The count is the max unless dlclose or failed dlopen created gaps.  */
+  /* It is rare that we have gaps; see elf/dl-open.c (_dl_open) where
+     we fail to load a module and unload it leaving a gap.  If we don't
+     have gaps then the number of modids is the current maximum so
+     return that.  */
   if (__glibc_likely (!GL(dl_tls_dtv_gaps)))
     return GL(dl_tls_max_dtv_idx);