[DSLX] Remove unneeded transaction in ParseTerm.
[DSLX] Remove unneeded transaction in ParseTerm.

Transactions (i.e. backtracking points) should be established on the _caller_
side, and _callee_ productions should fail as needed to perform their function
of parsing their grammar rule.

PiperOrigin-RevId: 391329440

google/xls,google/xls,google/xls,google/xls,google/xls,google/xls