Remove the need to update var/gradle_dependencies_version

Currently we need to update var/gradle_dependencies_version each time gradle-dependencies-list.txt is updated.

If you change gradle-dependencies-list.txt without updating var/gradle_dependencies_version, then you can easily end up with the wrong list of gradle dependencies being used in a build.

To avoid this we should see if we can make the gradle dependencies be fetched again automatically when gradle-dependencies-list.txt has been updated, without the need to update var/gradle_dependencies_version.