[gardening][Parse] Remove 2 unused flags in Parser (#4743)
* [Parse] Remove unused GreaterThanIsOperatorRAII. NFC
Last usage was removed in 68af974227d9a1c443150f9c28268a9d7485d915.
* [Parse] Remove unused ArgumentIsParameter flag. NFC
Last usage was removed in 4e4173f2e6f3bf550e7585b684b58792df6c8963