Bug 1613601 - Remove browser/components/build/Makefile.in. r=dmajor

The only remaining thing in this Makefile is a reset of
EMBED_MANIFEST_AT, which only has an effect when building a shared
library or executable, but browser components haven't built a shared
library since bug 1302855.

Differential Revision: https://phabricator.services.mozilla.com/D61792

--HG--
extra : moz-landing-system : lando

Author: glandium