Deprecate ':remove()' pseudo-class

Both `:remove()` pseudo-class and `remove` pseudo-property works the same, but the pseudo-property usage seems more recommended as it is related to "actions" which should be applied to elements, since pseudo-classes is more about elements matching.

Deprecation may be implemented in two steps:
1. mark the `:remove()` pseudo-class as deprecated but still supported
2. remove support of the pseudo-class