USE statements syntax in documenation is odd

[Roland Haas]

Currently the param.ccl parser will accepts things like:

USES REAL SomeReal ""
{
}

which is (almost, the docs would require a default value) correct according to the documentation (https://www.einsteintoolkit.org/usersguide/UsersGuidech12.html#x17-185000D2.3.2) but does not make much sense for USES (it is sensible for EXTENDS).

Similarly the len, STEERABLE and ACCUMULATOR options make no sense for USES or EXTENDS, and stead only make sense for actual declarations, while AS really only makes sense for USES and EXTENDS.