Buildozer remove_if_equal command should handle list values

[tetromino]

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')