[BUGFIX] Failing test in caching framework memcache backend

Bugfix #30162 changed the memcache handling to not throw an exception but
insert a sys_log entry instead in case of connection problems. The patch
removes the according unit test that broke with the
change, since the call to the static syslog is untestable.

Change-Id: I9891a4e571be6f99d86d335dd8bf1786fac87d1e
Resolves: #35897
Releases: 6.0, 4.7, 4.6, 4.5
Reviewed-on: http://review.typo3.org/10328
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn