Delete pin table

The pin table was brought over from dalvik but not really needed
since ART doesn't support pinning in movable spaces. The only
thing it did was hold objects live for JNI functions.
This shouldn't be necessary since people keep jni references to
these objects or else they could never release the elements.

Bug: 17456946

(cherry picked from commit a967c62e)
Change-Id: Ibed0d029157ffb9e75ecd80d4d544d690986c090