Don't create an object library for Python wrapping

It requires CMake >= 2.8.8 and avoids duplication of ~5 lines of code
anyways, so it isn't needed.

Change-Id: Idbc6bf192a31692788cf7c259cd749b32f85a778
Merge topic 'unified-bindings-no-object-library' into master

179c7551 Don't create an object library for Python wrapping