sql: fix memory leak in SQL parser for column default rule

If non-terminal symbol is referenced in C code then destructor for
expression is not called. Thus we don't need to duplicate. Otherwise we
got a memory leak.

See https://www.sqlite.org/cgi/src/doc/trunk/doc/lemon.html#destructor

Close #9159

NO_DOC=bugfix
NO_TEST=tested by debug ASAN CI (to be turned on)