Clean up some redundant or otherwise suspect code

Clean up some redundant or otherwise suspect code

* java/org/gnu/emacs/EmacsOpenActivity.java (onCreate):
Don't check if URI is non-NULL, for instanceof checks this
also.

* java/org/gnu/emacs/EmacsSafThread.java (accessDocument1):
Don't check !writable twice.

* java/org/gnu/emacs/EmacsService.java (documentIdFromName):
Designate this function as public, since it is called
through JNI.