fixed bug in combined intdivrem testvector extract script

Created by: kevindkim723

-old script skips first 2 lines in rv32m case, new script only skips first line

• prior code skipped every other line in the reference file, so it only generated half the test vectors, with half of them having the wrong answer
• prior code also opened test vector file to be written to in "append" mode, and I changed to write mode (so that the script overwrites instead of adding to an existing file)