Use one mizip for all

The new minzip did not compile in older trees due to needing
mmap64. For older trees we will just use mmap instead. Remove all
files and code pertaining to minzipold. Updater should now build
properly in older trees as well.

Eliminate use of PLATFORM_VERSION in favor of PLATFORM_SDK_VERSION
which should be more consistent and reliable.

Change-Id: I38d2b604a73d1b17a2072c7d60e990b81ece0c10