Remove ProcessState::mArgc,mArgV,mArgLen

These look like historical oddities, and weren't really being
used for anything useful.

Process:setArgV0 was being called by android.util.Process, but
that functionality can be moved directly into the implementation
of that class.

bug: 13647418

Change-Id: I216c8f8a4c065f0cf3a61f19f9e32decd26f93f6