Removed calls to find Boost/use it

The Avogadro application has never made use of Boost, and quite probably
will not do so.

Change-Id: I3974a774fa196f42ffd11bb147477fa8e3204a44
Merge branch 'remove-find-boost'

Change-Id: I2e0415f82215fdaa1caa528cf0f52eaf4f2539a9