Remove the check for source apk file size

The file deletion when finding that the source apk file size
was different than what was stored in SharedPreferences causes a race
condition when multiple processes are executing this code, where one
process could erase the secondary zip file while a different process had
already started to create the zip file.  This check is unnecessary and
has been removed.

Also, changed the parameter for getting the SharedPreferences to
Context.MODE_MULTI_PROCESS, which forces a re-read of the key/value
pairs from the file.

This should also fix the original bug b/12550057.

Bug: 12594955
Bug: 12550057
Change-Id: I53f4bca0d03a5737d802509274520a78effcf228