vendorcode/amd/agesa: Remove unused helper.c file

The contents of these files were guarded by a check for the _MSC_VER
macro, which we don't use.

Change-Id: Ic595c8e6284c54e1449cf21e0cebee8c9ce7c682
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/7670
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Tested-by: build bot (Jenkins)