RISC-V: Adjust test case due to vf[sz]ext.vf4 overlap

Remove the xfail due to vf4 changes.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/pr112431-16.c: Remove xfail.
	* gcc.target/riscv/rvv/base/pr112431-17.c: Ditto.

Signed-off-by: Pan Li <pan2.li@intel.com>