Deprecate doc profile?

[ehuss]

The doc profile currently is not used for anything. Is that intentional? Currently it is assigned to the Unit used for running rustdoc, but rustdoc does not use any of the flags from the profile. There are ~24 crates on crates.io that set it for whatever reason.

If it doesn't have a purpose, should we add a deprecation warning? Just remove it from the documentation?

[matklad]

Adding a deprecation warning and removing from the docs sounds good to me!