TTY: VT, remove unused variables

drivers/tty/vt/vt.c:892:2: warning: Value stored to 'old_screen_size' is never read
        old_screen_size = vc->vc_screenbuf_size;
        ^                 ~~~~~~~~~~~~~~~~~~~~~
drivers/tty/vt/vt.c:890:2: warning: Value stored to 'old_cols' is never read
	old_cols = vc->vc_cols;
	^          ~~~~~~~~~~~

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>