the parser couldn't parse `1=2 not between 3 and 5`
after `2` it expected only NOT2_SYM, but not NOT_SYM
(visible from the sql_yacc.output file), which resulted in
Syntax error ... near 'not between 3 and 4'

The parser was confused by a rather low NOT_SYM precedence and
%prec BETWEEN_SYM didn't resolve this confusion.

As a fix, let's remove any %precedence from NOT_SYM and
specify %prec explicitly in the only place where it matters for NOT_SYM.

In other places, such as for NOT BETWEEN, NOT_SYM won't have a
precedence, so bison won't be confused about it.