Remove define of mach_vm_region from mach_vm_compatibility.h.

mach_vm_region() is not called in the Breakpad codebase.

Patch by: blundell@chromium.org

R=qsr@chromium.org

Review URL: https://breakpad.appspot.com/643002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1223 4c0a9323-5329-0410-9bdc-e9ce6186880e