Buildozer remove_if_equal command should handle list values

Currently, it only supports attributes whose type is string or label: see https://github.com/bazelbuild/buildtools/blob/master/edit/buildozer.go#L420

It would be useful to have a single command for removing list-valued attributes such as deps. (The current alternative would be a script that e.g. uses `buildozer 'print name' 'print deps'` and post-processes the output to collect the list of targets on which to run `buildozer 'remove deps'`)

Read edit/buildozer.go around line 420 and trace how remove_if_equal handles string and label attributes. Extend the command's behavior for list-valued attributes such as deps, and verify that matching list entries are removed while other values remain.

Written by the indexing model from the issue text.