Remove gnu_unique_object configure test.

There is a configure test for assembler support for the
gnu_unique_object symbol type.  This support was added in binutils
2.20, so is present in all versions supported for building glibc.

Thus, I think the configure test can be removed; this patch does so.
Now, there is a caveat that the gas NEWS entry refers to this as a
feature for GNU/Linux targets.  But the condition is use of
ELFOSABI_GNU or ELFOSABI_NONE.  ELFOSABI_GNU covers Hurd as well as
GNU/Linux (as was the case with the older ELFOSABI_LINUX name), and
ELFOSABI_NONE means this is effectively OS-independent.  Furthermore,
I think a correct binutils port for any glibc target ought to support
this feature for use with glibc; glibc supports this as an
OS-independent feature (the configure test is only about glibc
testcases).

Tested for x86_64 (testsuite, and that installed shared libraries are
unchanged by the patch).

	* configure.ac (libc_cv_asm_unique_object): Remove configure test.
	* configure: Regenerated.
	* config.h.in (HAVE_ASM_UNIQUE_OBJECT): Remove #undef.
	* elf/tst-unique1.c (do_test) [HAVE_ASM_UNIQUE_OBJECT]: Make code
	unconditional.
	* elf/tst-unique1mod1.c [HAVE_ASM_UNIQUE_OBJECT]: Likewise.
	* elf/tst-unique1mod2.c [HAVE_ASM_UNIQUE_OBJECT]: Likewise.
	* elf/tst-unique2.c (do_test) [HAVE_ASM_UNIQUE_OBJECT]: Likewise.
	(do_test) [!HAVE_ASM_UNIQUE_OBJECT]: Remove conditional code.
	* elf/tst-unique2mod1.c [HAVE_ASM_UNIQUE_OBJECT]: Make code
	unconditional.
	* elf/tst-unique2mod2.c [HAVE_ASM_UNIQUE_OBJECT]: Likewise.