Staging: hv: delete mousevsc_api.h

This file is only used by one .c file (hv_mouse.c) so just move the
whole thing into that file.

Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>