Unnecessary (the linker gets the right library from pkgconfig anyway)
and breaks slotted Lua. See Bug #761511 for details.

--- a/src/gui-qt/highlight.pro
+++ b/src/gui-qt/highlight.pro
@@ -39,7 +39,6 @@
 unix {
     DESTDIR = ../
     LIBS += -L.. -lhighlight
-    LIBS += -llua
     CONFIG += link_pkgconfig
     PKGCONFIG += lua