Remove `rlang_muffle`

[lionel-]

We've never used it (https://github.com/search?q=org%3Acran%20rlang_muffle&type=code) and installing a restart has a small performance impact: r-lib/lifecycle#198

[lionel-]

oops of course should look at the wrapper, not the restart name: https://github.com/search?q=org%3Acran%20cnd_muffle&type=code

It is used quite a bit.