Finish ManagedComBridge build changes on Linux

ManagedComBridge is now built and installed as a part of COM.

This is a fixup for:

  911336a "Adjust to changes in the way ManagedComBridge is made on Linux"

Change-Id: I1aa1e3fc95bbc445d918b1af9a4fa5d81ba56fea
Add environ-xulrunner to the list of files to install on Linux

environ-xulrunner was created in 61f7435

This commit was cherry picked from d37a038 on support/7.0-Linux

Change-Id: Ic69cf873c0580d75a1f95f4f3e34d423dc6336fb
Don't do any building during the install phase on Linux

This was causing a package build failure on Lucid, because the environment
is not set up for building during the install phase.

This commit was cherry picked from 86d09d9 on support/7.0-Linux

Change-Id: I3ae0741c77b89312385f93d2486e3442986c1b0f