Elasticsearch: Remove the 2.14.x and 2.15.x columns

Remove these table columns as they correspond to EOL Gerrit versions,
which are no longer supported.

Keep the 2.4.x table line, as it still holds information about supported
Gerrit versions.

Fix the markdown-lint warning about doubling a blank line in that file.

Change-Id: I803bbee91389aea5010e9f80091dfe643a7040ec
1 file changed