Don't redefine ROUNDING_TESTS_* in math/test-*-vlen*.h.

This patch completes the move of ROUNDING_TESTS_* macros to typo-proof
conventions by stopping redefining them in test-*-vlen*.h.  Instead,
libm-test-driver.c is made to check TEST_MATHVEC when setting
non-to-nearest rounding modes.

Tested for x86_64.

	* math/test-double-vlen2.h: Don't include <math-tests-rounding.h>.
	(ROUNDING_TESTS_double): Remove.
	* math/test-double-vlen4.h: Don't include <math-tests-rounding.h>.
	(ROUNDING_TESTS_double): Remove.
	* math/test-double-vlen8.h: Don't include <math-tests-rounding.h>.
	(ROUNDING_TESTS_double): Remove.
	* math/test-float-vlen16.h: Don't include <math-tests-rounding.h>.
	(ROUNDING_TESTS_float): Remove.
	* math/test-float-vlen4.h: Don't include <math-tests-rounding.h>.
	(ROUNDING_TESTS_float): Remove.
	* math/test-float-vlen8.h: Don't include <math-tests-rounding.h>.
	(ROUNDING_TESTS_float): Remove.
	* math/libm-test-driver.c (IF_ROUND_INIT_FE_DOWNWARD): Check
	!TEST_MATHVEC here.
	(IF_ROUND_INIT_FE_TOWARDZERO): Likewise.
	(IF_ROUND_INIT_FE_UPWARD): Likewise.