miscelaneous fixes on syncing, rpc and responding to peer's sync related requests (#3827)

- there was a bug in responding range blob requests where we would incorrectly label the first slot of an epoch as a non-skipped slot if it were skipped. this bug did not exist in the code for responding to block range request because the logic error was mitigated by defensive coding elsewhere
- there was a bug where a block received during range sync without a corresponding blob (and vice versa) was incorrectly interpreted as a stream termination
- RPC size limit fixes.
- Our blob cache was dead locking so I removed use of it for now.
- Because of our change in finalized sync batch size from 2 to 1 and our transition to using exact epoch boundaries for batches (rather than one slot past the epoch boundary), we need to sync finalized sync to 2 epochs + 1 slot past our peer's finalized slot in order to finalize the chain locally.
- use fork context bytes in rpc methods on both the server and client side

beacon_node/store/src/hot_cold_store.rs

@@ -503,9 +503,9 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
     }
 
     pub fn get_blobs(&self, block_root: &Hash256) -> Result<Option<BlobsSidecar<E>>, Error> {
-        if let Some(blobs) = self.blob_cache.lock().get(block_root) {
-            Ok(Some(blobs.clone()))
-        } else if let Some(bytes) = self
+        // FIXME(sean) I was attempting to use a blob cache here but was getting deadlocks,
+        // may want to attempt to use one again
+        if let Some(bytes) = self
             .hot_db
             .get_bytes(DBColumn::BeaconBlob.into(), block_root.as_bytes())?
         {