Deprecate ':remove()' pseudo-class

[slavaleleka]

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

[krystian3w]

How will this affect projects that do not convert this in :style(remove: true)?

[ameshkov]

Generally, it won't affect anyone. The rules that use :remove() will be automatically converted to the ExtCSS syntax, we just don't want to have this logic in two places (ExtCSS and CoreLibs/tsurlfilter).