Revert "arm64/nterp: Shorter `if-{cond}` opcode handlers."

This reverts commit 1e2a904234232406cfe9509e4ed1a605c1169117.

Reason for revert: After making the opcode dispatch shorter
recently, the redirection from `if-{cond}` to `if-{cond}z`
is no longer needed as the code fits in the 64B handler.

Test: testrunner.py --target --64 --interpreter
Flag: EXEMPT PURE_REFACTOR
Change-Id: I3f2cd9590a0cbd7fe5fca41b7dd0909724314306