Core/Misc: Various dynspawn cleanup and refactors split off from pooling rewrite:

- Map::RemoveRespawnTime(SpawnObjectType, LowType, doRespawn) split into Map::Respawn and Map::RemoveRespawnTime, without the extra boolean
- Map::RemoveRespawnTime(RespawnInfo*) merged into Map::DeleteRespawnInfo(RespawnInfo*) and is now private
- Map::DeleteRespawnInfo(void) renamed to Map::UnloadAllRespawnInfos to properly describe what it does
- Map::ProcessRespawns now actually saves the delayed respawn time to DB if the respawn was delayed
- Map::AddRespawnInfo now takes const reference, and returns success as a boolean
- Map::AddRespawnInfo no longer offers an unused "replace" parameter
- Map::DeleteRespawnInfo no longer offers a variety of unused private overloads
- Map::SaveRespawnTime no longer offers a tantalizing writeDB parameter. Parameter is now called "startup" to properly describe what it does.
- Map::SaveRespawnInfoDB now takes RespawnInfo reference instead of all the various fields. Still public because compatibility mode. QQ.
- Map::GetWorldObjectBySpawnId sanitized
- Map::GetXRespawnTime methods sanitized to all go through Map::GetRespawnTime

(cherry picked from commit d60082ae86)

src/server/scripts/Commands/cs_misc.cpp

@@ -1983,7 +1983,7 @@ public:
             uint32 const gridId = Trinity::ComputeGridCoord(player->GetPositionX(), player->GetPositionY()).GetId();
             for (RespawnInfo* info : data)
                 if (info->gridId == gridId)
-                    player->GetMap()->RemoveRespawnTime(info, true);
+                    player->GetMap()->Respawn(info->type, info->spawnId);
         }
 
         return true;

src/server/scripts/Northrend/Naxxramas/boss_thaddius.cpp

@@ -337,8 +337,8 @@ struct boss_thaddius : public BossAI
             me->SetReactState(REACT_PASSIVE);
 
             // @todo these guys should really be moved to a summon group - this is merely a hack to make them work in dynamic_spawning
-            instance->instance->RemoveRespawnTime(SPAWN_TYPE_CREATURE, 130958, true); // Stalagg
-            instance->instance->RemoveRespawnTime(SPAWN_TYPE_CREATURE, 130959, true); // Feugen
+            instance->instance->Respawn(SPAWN_TYPE_CREATURE, 130958); // Stalagg
+            instance->instance->Respawn(SPAWN_TYPE_CREATURE, 130959); // Feugen
         }
 
         void UpdateAI(uint32 diff) override