USB: serial: metro-usb: remove the .h file

A driver doesn't need a .h file just for simple things like vendor ids
and a private structure.  So move it into the .c file instead, saving
some overall lines.

Cc: Aleksey Babahin <tamerlan311@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>