x/tools/cmd/goimports,gopls: avoid deprecated symbols and/or packages

[findleyr]

Skimming the codebase, it look like we don't consider API deprecation in goimports. That is surprising.

We should avoid deprecated symbols and packages as import candidates.

Edit: context is #70717, where a user imported x/exp/maps by accident. (Though, will note that x/exp/maps is not currently deprecated).

CC @pjweinb

[pjweinb]

https://go-review.git.corp.google.com/c/tools/+/641776 fixes this, I think. See TestDeprecated70736().