After an entity has a component removed from it, the apply function wasn't removing it from the removed list.
This had weird side-effects like the inability to readd components after they were removed.
For example:
entity:give(Foo):apply()
entity:remove(Foo):apply()
entity:give(Foo):apply() -- This line would fail to add the Foo component again.
The documentation states that Entity:has will return false if the component doesn't exist and true if it does.
However, the previous behaviour was to return nil if the component doesn't exist.
