Remove ancient Puppet versions from matrix.

With PE 3.2 out of the door shipping with 3.4.3 I think it's time to
shrink the matrix and get rid of 3.1 and 3.2. PE 3.x customers should
just upgrade to 3.2, OS users should really be on 3.3+ by now.
Merge pull request #262 from daenney/shrink-test-matrix

Remove ancient Puppet versions from matrix.