Remove unused grantors function in MQDescriptor am: 90d01ef298 am: b5838257e7 am: 2142e0d1da am: d0f4bb9e08

Original change: https://android-review.googlesource.com/c/platform/system/libhidl/+/1493219

Change-Id: I62341d46a21f16913a0d57f9e4f403b0fde992a4