Remove fixed-size literal buffer from ecpg's lexer (same

fix recently applied to backend's lexer).  I see that YY_USES_REJECT
still gets defined for this lexer, which means it's going to have trouble
parsing really long tokens.  Not sure if it's worth doing anything about
that or not; I don't have the interest right now to understand why
ecpg's additions to the syntax cause this problem...