Bug 978012 - [email] Remove dead/obsolete GELAM-built JS blobs and fix GELAM to clean out ext/ before installing. r=mcav

land https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/289
Merge pull request #16793 from asutherland/email-gelam-cleanup

Bug 978012 - [email] Remove dead/obsolete GELAM-built JS blobs and fix GELAM to clean out ext/ before installing. r=mcav