Remove full_eviction mode from ep_perfsuite

The full eviction variant of ep_perfsuite is essentially a waste of time (and prone to intermittent failures).

The perfsuite tests run with persistence disabled (see the call to stop_persistence at the start of perf_latency. As a consequence the tests sometimes fail, as items are essentially getting evicted from memory (and put onto the disk queue) but the queue will never be persisted, and hence item counts will not be correctly updated. (Note: this relates to the issues found in MB-19501).

Additionally, even if the tests did work, given we disable persistence there's essentially no value in the results output as they aren't representative of what full eviction operations might cost (as no disk overhead is included).

For these reasons I'm disabling the full eviction mode of ep_perfsuite. While in the abstract it would be useful to have numbers from this suite for full eviction, it requires a reasonable amount of work to make work in a sensible way.