No need to use extra table for persistent header cache state record

why:
  Slot zero can do. This allows deleting that table wholesale when needed
  once thatfeature is available.

nimbus/db/storage_types.nim

@@ -24,8 +24,7 @@ type
     dataDirId = 7
     safeHash = 8
     finalizedHash = 9
-    beaconState = 10
-    beaconHeader = 11
+    beaconHeader = 10
 
   DbKey* = object
     # The first byte stores the key type. The rest are key-specific values
@@ -87,11 +86,6 @@ func hashIndexKey*(hash: Hash32, index: uint16): HashIndexKey =
   result[32] = byte(index and 0xFF)
   result[33] = byte((index shl 8) and 0xFF)
 
-func beaconStateKey*(u: uint8): DbKey =
-  result.data[0] = byte ord(beaconState)
-  result.data[1] = u
-  result.dataEndPos = 1
-
 func beaconHeaderKey*(u: BlockNumber): DbKey =
   result.data[0] = byte ord(beaconHeader)
   doAssert sizeof(u) <= 32

nimbus/sync/beacon/worker/db.nim

@@ -19,8 +19,8 @@ import
   ../worker_desc,
   ./headers_unproc
 
-const
-  LhcStateKey = 1.beaconStateKey
+let
+  LhcStateKey = 0.beaconHeaderKey
 
 # ------------------------------------------------------------------------------
 # Private helpers