Revert "Make it easier to track differences between Maven and Gradle build scan enhancements"

This reverts commit 2ea4d6d.

This change broke Gradle configuration cache support due to the capture of the `Gradle` instance
in the background closure for `captureGitMetadata`. While it is possible to remove this capture
by extracting a separate static method, it seems simpler overall to revert back to the previous
all-static implementation.

Author: bigdaz