Remove global variables from ProcessState.

These weren't really being used and they make it
very hard to reason about who looks at command line
arguments.

Processes started via app_process (this includes all
zygote forks and the system_server) can get information
about command line arguments from the AndroidRuntime
class, which is available via a call to
AndroidRuntime::getRuntime.

bug: 13647418

Change-Id: I6f92680c3619a68c6d4b0995db4cdc9adc788e36