Properly run emacsclient under Android if DISPLAY is set

Properly run emacsclient under Android if DISPLAY is set

* java/org/gnu/emacs/EmacsPixmap.java (EmacsPixmap): Make
dimensions final, since they are never changed after the
constructor.

* lib-src/emacsclient.c (decode_options): If --display is not
provided, always set display to `android' even if DISPLAY is
provided.

* lisp/net/browse-url.el (browse-url): Cease setting DISPLAY
under Android.

* src/callproc.c (getenv_internal, make_environment_block):
Don't afford DISPLAY special treatment under Android.