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

GerritCodeReview/homepage,GerritCodeReview/homepage,GerritCodeReview/homepage,GerritCodeReview/homepage,GerritCodeReview/homepage