Use simpler syntax in grammar names

Things like `token package_declarator:sym<grammar>` become `token package_declarator:grammar`

The only nits here are that the line
```<?sigil> <var=.LANG('MAIN', 'term:variable')>```
which seems like it should work, doesn't in NQP, and must be:
```<?sigil> <var=.LANG('MAIN', 'term:variable<1>')>```
and that we can't use
```method package_declarator:grammar($/)```
but instead
```method package_declarator:grammar ($/)```
because NQP (and Perl) will think ($/) is the value of the :grammar colonpair