IOT-1302 Thread-unsafe code in oicgroup.c

IOT-1302 Thread-unsafe code in oicgroup.c

Remove potential thread safety bugs in oicgroup
Make RD mutex implementation work on Windows
Remove duplicate mutex implementations

Change-Id: Ie47b24619a10ab3d9cab2d421f3a7d8be7ac7b55
Signed-off-by: Dave Thaler <dthaler@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/11941
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: David Antler <david.a.antler@intel.com>
Reviewed-by: Uze Choi <uzchoi@samsung.com>
Reviewed-by: Habib Virji <habib.virji@samsung.com>
Reviewed-by: jihwan seo <jihwan.seo@samsung.com>