Remove processSerializedRequest from BlobstoreThriftProcessor
Remove processSerializedRequest from BlobstoreThriftProcessor

Summary:
This diff is a part of a series that aims to deprecate `AsyncPocessor::processSerializedRequest`. This is [step 1.4](https://fb.quip.com/cqP7Ap4UPLY8#temp:C:aAN7eafcef22d9042a3ab06073ae) of [this plan](https://fb.quip.com/cqP7Ap4UPLY8).

At this point **every** AsyncProcessor implements `processSerializedCompressedRequestWithMetadata`, and we can remove usages of `processSerializedRequest`.

Reviewed By: ycking21

Differential Revision: D38662642

fbshipit-source-id: bcad26bf2a626406ecf7879fd8a10c697efca92b

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