As can be seen in [1] the patches to KWin were in CVS HEAD before the
protocol got standardized and it never got any adoption. It's neither in
the NETWM spec, nor implemented in Qt4 nor in Qt5. KWin did not even add
the protocol to the NET::Supported property.

Thus it doesn't make much sense to keep a protocol which nobody speaks.

Still the code around the protocol is kept and also the names are kept.
Only difference is that Client::takeActivity got removed and the code
moved to the only calling place in Workspace. Motivated by that change
the enum defined in utils.h is moved into Workspace, it's turned into
a proper QFlags class and used as a type in the method argument instead
of a generic long.

[1] https://mail.gnome.org/archives/wm-spec-list/2004-April/msg00013.html

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