Schedule removing unideal features: move them to `incompatible`

[jerrymarino]

A lot of the features we added here were only features / conditional because they were in-development and I often want to encourage people to work iteratively. Some features should eventually transition to be removed to reduce complexity and keep rules_ios lightweight

Because of this - we have some features that should be removed - and we have to maintain complexity while they stay around. My proposal is:

1. develop a feature - by adding --features apple.enable_awesome_feature
2. default the feature to enabled - and then
   2a. if the feature isn't deemed ideal to keep around, then schedule it for removal.
   2b. the feature scheduled for should follow Bazel's incompatible pattern - to encourage
   people to flag issues with us.:
   apple.enable_awesome_feature -> apple.incompatible_disable_awesome_feature

Related is this thread about enabling defaults: #630