Remove `custom_score` and `custom_boost_factor` queries

`custom_boost_factor` and `custom_score` were deprecated in `0.90.5`
and their documentation was removed already in `1.0`. This commit
removes all support for those queries since they are supercede by
`function_score`.
[Docs] Remove `custom_score` from documentation and add a migration
section.
[DOCS] Fix typo in rename_pattern in snapshot/restore documentation
Added test #5078
[DOC] Updated the Ruby gem version for Elasticsearch 0.90.x
Beefed up DeleteByQueryTests to run not just against a single document
[TEST] disabled replicas in validate query test