[RISCV] Remove uses of sed from compress-opt-branch.ll. NFC

sed was being used to use the same test functions with eq/ne branch
condition.

This commit duplicates the test functions so that we have a version
with each condition. This allows us to remove 2 RUN lines.

I plan to add a Zca testing to this file which now requires 1 new
RUN line instead of 2.

Author: topperc