Qt5XmlPatterns is not actually used, but build will fail if it's missing.

Gentoo-bug: 564316

--- src/src.pro
+++ src/src.pro
@@ -4,8 +4,7 @@
 TARGET = oauth2plugin
 DESTDIR = lib/signon
 QT += core \
-    network \
-    xmlpatterns
+    network
 QT -= gui
 CONFIG += plugin \
     build_all \