Move memallocmanaged up into HostOnlyCUDAMemoryManager
Move memallocmanaged up into HostOnlyCUDAMemoryManager

Any implementations of EMM plugins that are based on
HostOnlyCUDAMemoryManager probably should not have to implement
memallocmanaged - moving the method up the hierarchy facilitates this.

gmarkall/numba,gmarkall/numba,seibert/numba,cpcloud/numba,IntelLabs/numba,stuartarchibald/numba,stuartarchibald/numba,stonebig/numba,IntelLabs/numba,stuartarchibald/numba,numba/numba,IntelLabs/numba,numba/numba,IntelLabs/numba,seibert/numba,seibert/numba,stuartarchibald/numba,cpcloud/numba,gmarkall/numba,stonebig/numba,IntelLabs/numba,numba/numba,gmarkall/numba,gmarkall/numba,cpcloud/numba,seibert/numba,cpcloud/numba,cpcloud/numba,numba/numba,seibert/numba,stonebig/numba,stonebig/numba,numba/numba,stonebig/numba,stuartarchibald/numba