[Qt] Fix make install on Windows

https://bugs.webkit.org/show_bug.cgi?id=94816

Reviewed by NOBODY (OOPS!).

This old left-over rule for Windows to add dlltarget to INSTALLS caused
various bugs: WebCore's Makefile had an actual install target that
tried to install the WebCore static library and it also screwed up
api.pri's install rule by overriding what is usually set up for qt
modules, i.e. the install path was missing INSTALL_ROOT. We don't need
these rules at all, the default qmake features take care of setting up
target install rules accordingly.

* WebCore.pri:

0 files changed, 0 insertions, 0 deletions