[releng] Update Mylyn Wikitext update site URL
Since March 2017, it is distributed via a separate update site that
doesn't have a "latest" version. C.f. bug 513498.
Two notes:
* The Mars target (egit-4.5) is broken as of today: easymport.tpd
no longer works; the bundle is no longer in the e4 snapshot update
site. I don't know where we might get it from.
* Wikitext is used only to generate org.eclipse.egit.doc. It's a
build-time dependency only; it should not be in the target at all.
However, trying to refactor this along the lines shown in [1]
will be done later (and not in a maintenance branch). One problem
with such a conversion might be that the latest version available
in the maven repository is wikitext 2.9.0-SNAPSHOT.
[1] http://help.eclipse.org/oxygen/index.jsp?topic=%2Forg.eclipse.mylyn.wikitext.help.ui%2Fhelp%2FMarkup-Conversion.html
Change-Id: If4668f14be43dba19b6d2321f42a1a2f7e646ce6
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>