testsuite: LoongArch: Remove from btrunc, ceil, and floor effective target allowlist

testsuite: LoongArch: Remove from btrunc, ceil, and floor effective target allowlist

Now that C default is C23, so we can no longer use LSX/LASX instructions
for these operations as the standard disallows raising INEXACT
exceptions.  So LoongArch is no longer suitable for these effective
targets.

Fix the test failures on gcc.dg/vect/vect-rounding-*.c.  For the old
standards or -ffp-int-builtin-inexact we already provide test coverage
with gcc.target/loongarch/vect-ftint.c.

gcc/testsuite/ChangeLog:

	* lib/target-supports.exp
	(check_effective_target_vect_call_btrunc): Drop LoongArch.
	(check_effective_target_vect_call_btruncf): Likewise.
	(check_effective_target_vect_call_ceil): Likewise.
	(check_effective_target_vect_call_ceilf): Likewise.
	(check_effective_target_vect_call_floor): Likewise.
	(check_effective_target_vect_call_floorf): Likewise.
	(check_effective_target_vect_call_lfloor): Likewise.
	(check_effective_target_vect_call_lfloorf): Likewise.