Update usx schema

[kavitharaju]

• Pulled the latest RNG Grammar from usfm-bible/tcdocs
• Testing again, the USX generation and validation
  • Removed the older list of doubtful USXs, including them also in the test now
  • 181 positive samples from testsuite have been used for test
  • Following is the results of testing, as of now. Planning to investigate the failures and make changes as required

Validating generated USX against the updated RNG grammar from usfm-bible/tcdocs

66 Failed 115 Passed

Validating USX samples in testsuite itself, against the RNG grammar

44 Failed 133 Passed (Martin's Stat is 159/258 Passing for him)

Comparing generated USX against USX samples in the testsuite

157 Failed 24 Passed :smile: