perf(annotations): increased performance of egef_annotations

The default behaviour of elgg_get_entities_from_annotations was
different from all other elgg_get_entities_from* functions.
This also caused a performance issue on large databases

Fixes #6638
Merge pull request #7600 from mrclay/jeabakker-elgg-get-entities-from-annotations

perf(annotations): increased performance of egef_annotations