Remove graph pattern based partitioners (#196)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/196

Since we migrated to source_partition based logic for partitioning we don't need graph patterns anymore.
If something goes wrong with the source_partition we will revive this but until then no need for this.

Moves DQ partitioner to QNNPACK since it is still using it.

Reviewed By: mcr229

Differential Revision: D48766742

fbshipit-source-id: 23461791a08477b7a5710772d77f029fc23241a3