Drivers: hv: Remove leftover support for old Hyper-V versions

When removing support for running Linux guests on Windows Server
2008/2008R2 and Windows 7, one area was missed due to the code
comment spelling "2012" incorrectly. Remove that functionality now.

Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>