Fix a number of syntax errors in contrib modules' uninstall scripts.

Fix a number of syntax errors in contrib modules' uninstall scripts.
Most of the changes add the mandatory USING clause to DROP OPERATOR
CLASS statements.  DROP TYPE is now DROP TYPE CASCADE; without
CASCADE a DROP TYPE fails due to the circular dependency on the
type's I/O functions.  The DROP FUNCTION statements for the I/O
functions have been removed, as DROP TYPE CASCADE removes them
automatically. Patch from Michael Fuhr.