Avoid overwrite warning using more specific method

[omus]

As of Julia 1.10 we receive warnings like the following when running Mocking.activate():

WARNING: Method definition activated() in module Mocking at /Users/cvogt/.julia/dev/Mocking/src/Mocking.jl:15 overwritten at /Users/cvogt/.julia/dev/Mocking/src/Mocking.jl:24.

As the method efinition overwrite is intentional here as we purposefully make use of invalidation to support @mock it would be best to silence this warning for end users.

We can use the Julia flag --warn-overwrite=no to do this (which is the default) but running Pkg.test() seems to enable this flag.

In order to silence this error message we're now avoiding overwriting an existing method and now we are instead just defining a more specific method which ends up having the same result but without the warning. We can however no longer cleanly support multiple calls to activate/deactivate as unless we want to utilize an arbitrarily deep type hierarchy. Due to this new restriction I've opted to deprecate both deactivate and activate(f) which I'm doubtful were used externally.

[omus]

Note we still see some of these warnings due to the multiple activate calls in test/activate.jl. Once the deprecated functions are no longer tested these warnings will disappear.

[nickrobinson251]

We use activate(f) extensively throughout our testing codebase at RAI, and removing it (as was done in the v0.8 release) prevents us from updating Mocking.jl

I think we're fine with the warnings WARNING: Method definition ... and would be happy to live with them in our tests for the convenience/safety of having the activate(f) method. What do you think about reinstating this method and have it redefine _activate(::Int), so that only activate(f) would give the warning, and activate() would be warning-free?

cc @omus