elf: Remove unused l_text_end field from struct link_map

It is a left-over from commit 52a01100
("elf: Remove ad-hoc restrictions on dlopen callers [BZ #22787]").

When backporting commmit 6985865b
("elf: Always call destructors in reverse constructor order
(bug 30785)"), we can move the l_init_called_next field to this
place, so that the internal GLIBC_PRIVATE ABI does not change.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>
(cherry picked from commit 53df2ce6)