[Hexagon] Remove incorrect intrinsic definition and invalid testcase

The intrinsic int_hexagon_S2_asr_i_vh was mapped to S2_asr_r_vh, which
is wrong. The testcase vasrh.select.ll was using an invalid immediate
for that intrinsic. This is not a proper testcase, since at the MIR
level such use of this intrinsic should never appear.

Together with 824b25fc, this completes the fix for llvm.org/PR44090.