Currently, the primitive `(~#)`, `(~R#)`, and `(~P#)` type
constructors are wired in to be exported from `GHC.Prim`. This has
some unfortunate consequences, however. It turns out that `(~#)` is
actually a legal infix identifier, so users can make use of unboxed
equalities in strange ways in user code (see #15209). The other two,
`(~R#)` and `(~P#)`, can't be used in source code, but they can be
observed with GHCi's `:browse` command, which is somewhat unnerving.

The fix for both of these problems is simple: just don't wire them
to be exported from `GHC.Prim`.

Test Plan: make test TEST="T12023 T15209"

Reviewers: bgamari, dfeuer

Reviewed By: bgamari, dfeuer

Subscribers: rwbarton, thomie, carter, dfeuer

GHC Trac Issues: #12023, #15209

Differential Revision: https://phabricator.haskell.org/D4801