CPack: Disable OS X PackageMaker by default (#13662)

As mentioned in commit 4693cf84 (Xcode: Detect new default locations of
Xcode 4.3 bits and pieces) PackageMaker was split out of Xcode 4.3 and
above into a separate Auxiliary tools package.  Since Xcode 5.0 or so,
Apple no longer distributes PackageMaker as part of the available
development tools so it can only be obtained from old packages.

Disable the CPACK_BINARY_PACKAGEMAKER option by default as is the case
for most other tool-dependent generators.