Remove configure test for assembler .text directive.

There is a configure test for assembler support for the .text
directive.

I suppose this test must have been aimed at some non-ELF platform or
non-GNU assembler.  Certainly the GNU assembler has had ELF-specific
architecture-independent handling for .text since version 2.2, and
generic non-ELF-specific support predates that.

This patch removes this test as obsolete.

Tested for x86_64 and x86 (testsuite, and that installed shared
libraries are unchanged by the patch).

	* configure.ac (libc_cv_dot_text): Remove configure test.
	(libc_cv_asm_set_directive): Use .text instead of
	${libc_cv_dot_text} in configure test.
	* configure: Regenerated.