graphics/zathura: Fix SQLITE option

There is no opt_MESON_ARGS_OFF helper and Zathura also does not
have an enable-sqlite option. It has an 'sqlite' feature which can
be turned on/off with the MESON_ENABLED helper.

SQLite support has been auto-enabled for ~7 months by always having
USES=sqlite in the port. Since the SQLITE option can now properly
turn that support off, enable it by default to not cause too many
surprises.