remove unnecessary empty build.gradle files (opensearch-project#4723)

* remove unnecessary empty `build.gradle` files

these have no impact, as the targets are added by the parent
`build.gradle`. thus they do not need to exist and are currently just
cluttering the workspace and confusing people trying to work in that
area.

see also the discussion on opensearch-build#99 for some details.

Signed-off-by: Ralph Ursprung <Ralph.Ursprung@avaloq.com>

* Revert removal of distribution/docker/docker-export/build.gradle

Signed-off-by: Kartik Ganesh <gkart@amazon.com>

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Signed-off-by: Ralph Ursprung <Ralph.Ursprung@avaloq.com>
Signed-off-by: Kartik Ganesh <gkart@amazon.com>
Co-authored-by: Kartik Ganesh <gkart@amazon.com>
Signed-off-by: Shivansh Arora <hishiv@amazon.com>

Author: 2 people