nir/opt_if: Fix opt_if_simplification when else branch has jump

nir/opt_if: Fix opt_if_simplification when else branch has jump

Consider the following case:

 if ssa_1 {
    block block_2:
    /* succs: block_4 */
 } else {
    block block_3:
    ...
    break
    /* succs: block_5 */
 }

 block block_4:
 vec1 32 ssa_100 = phi block_2: ssa_2

After block_3 extraction and reinsertion, phi->pred becomes invalid
and isn't updated by reinsertion since it is unreachable from block_3.

Call nir_opt_remove_phis_block before moving block to eliminate single
source phis after the if.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3282
Fixes: e3e929f8c342b32dc8f5296adf8fb337866fa40a
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5945>