Fielddata: Remove soft/resident caches.

These caches have no advantage compared to the default node cache. Additionally,
the soft cache makes use of soft references which make fielddata loading quite
unpredictable in addition to pushing more pressure on the garbage collector.

The `none` cache is still there because of tests. There is no other good
reason to use it.

LongFieldDataBenchmark has been removed because the refactoring exposed a
compilation error in this class, which seems to not having been working for a
long time. In addition it's not as much useful now that we are progressively
moving more fields to doc values.

Close #7443