Stop exporting, and stop using, functions marked as deprecated

Don't export `getUs` and `getUniqueUs`. `UniqSM` has a `MonadUnique` instance:

    instance MonadUnique UniqSM where
        getUniqueSupplyM = getUs
        getUniqueM  = getUniqueUs
        getUniquesM = getUniquesUs

Commandline-fu used:

    git grep -l 'getUs\>' |
        grep -v compiler/basicTypes/UniqSupply.lhs |
        xargs sed -i 's/getUs/getUniqueSupplyM/g

    git grep -l 'getUniqueUs\>' |
        grep -v combiler/basicTypes/UniqSupply.lhs |
        xargs sed -i 's/getUniqueUs/getUniqueM/g'

Follow up on b522d3a3f970a043397a0d6556ca555648e7a9c3

Reviewed By: austin, hvr

Differential Revision: https://phabricator.haskell.org/D220