Remove unused c: DB from MDB

src/store_mdb.c

@@ -3,7 +3,7 @@
 /**
  * Number of DBs defined. See MAIN_TABLE and LOOKUP_TABLE defines below.
  */
-#define N_DB 13
+#define N_DB 12
 
 /**
  * Memory map size.
@@ -112,7 +112,6 @@ typedef struct mdbstore_iter_t {
 /*          #ID pfx #DB label   #Flags  */ \
     ENTRY(  T_ST,   "t:st",     0               )   /* Key to ser. term */  \
     ENTRY(  SPO_C,  "spo:c",    DUPFIXED_MASK   )   /* Triple to context */ \
-    ENTRY(  C_,     "c:",       0               )   /* Track empty ctx TODO remove, unused. */   \
     ENTRY(  PFX_NS, "pfx:ns",   0               )   /* Prefix to NS */      \
     ENTRY(  IDK_ID, "idk:id",   0               )   /* ID key to ID */      \