Disable libm-test test name beautification for M_* constants.

math/gen-libm-test.pl has code to beautify names of various constants,
transforming the source form in libm-test.inc into the version
appearing in test names in libm-test-ulps files.

This has become decreasingly relevant over time for the M_* constants,
first as I changed the test names so only the arguments and not the
expected results appeared in them, then as tests have moved to
auto-libm-test-* so that automatically generated hex float constants
get used instead of M_* in test inputs.

This patch removes the beautification for all M_* constants.  Tested
x86_64 and x86 and ulps updated accordingly.  Even the one case where
this affected the name in the ulps files will disappear once complex
function tests are moved to auto-libm-test-*.

	* math/gen-libm-test.pl (%beautify): Remove M_* constants.
	* sysdeps/i386/fpu/libm-test-ulps: Update.
	* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.