pdl: let lint phase do all error handling

All errors in the code generator are internal bugs: the lint phase
should catch all illegal PDL constructs. This means that we can safely
crash when generating code (and then add more lints as needed to
prevent these crashes).

Bug: 230475552
Test: atest 'pdl_*'
Change-Id: If686acbb0f5edce0bae17611c4b1aa39dc27eac5