(Final!) fix-ups for Iddc778a28

* mediawiki: avoid spurious dep on libapache2-mod-php5
* Remove dupe apache site config for performance.wm.o

Change-Id: I042bd42a6887f5052dbb40636f0c9c1c88e3b8a7
Merge "(Final!) fix-ups for Iddc778a28" into production