Remove request_with_session/request_without_session from showCacheStats.php

Fix for I0ed1e87574 (42fcd43).

Since request_with_session/request_without_session were removed in the
mentionned commit, the maintenance/showCacheStats.php refuses to show
the other statistics.

Change-Id: I955cc537f8bc9116f759af5a5c3005aa7d60c83b