Remove -Bgroup configure test.

There is a configure test for the -Bgroup linker option whose results
aren't used anywhere.  This patch removes that test.

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

	* configure.ac (libc_cv_Bgroup): Remove configure test.
	* configure: Regenerated.
	* config.make.in (have-Bgroup): Remove variable.