[auto-publication] clean up old builds from the local maven repository

[grigoryk]

Currently, android-component builds accumulate in ~/.m2/repository/org/mozilla/components/. We really only need to keep the latest build.

The proposal here is:

• when we determine that local publication is necessary, purge all of ~/.m2/repository/org/mozilla/components before running publishToMavenLocal.

This assumes that ~/.m2/repository/org/mozilla/components only has things that are controlled via auto publication scripts, which I think is true.

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