[postgresql] Method checkLA(int c) is not target agnostic.

[kaby76]

I am now writing every port for the PostgreSQL grammar. But, I'm finding that the grammar is not Target Agnostic

In PostgreSQLLexer.g4, checkLA('-') cannot be target agnostic because not all languages can automatically cast a character literal (or string literal) '-' to an integer (e.g., JavaScript).

All actions in the .g4's must be parameterless method calls.