Always enable caches (#28527)

Nowadays, cache will be used on almost everywhere of Gitea and it cannot
be disabled, otherwise some features will become unaviable.

Then I think we can just remove the option for cache enable. That means
cache cannot be disabled.
But of course, we can still use cache configuration to set how should
Gitea use the cache.

modules/setting/cache.go

@@ -12,7 +12,6 @@ import (
 
 // Cache represents cache settings
 type Cache struct {
-	Enabled  bool
 	Adapter  string
 	Interval int
 	Conn     string
@@ -24,23 +23,19 @@ var CacheService = struct {
 	Cache `ini:"cache"`
 
 	LastCommit struct {
-		Enabled      bool
 		TTL          time.Duration `ini:"ITEM_TTL"`
 		CommitsCount int64
 	} `ini:"cache.last_commit"`
 }{
 	Cache: Cache{
-		Enabled:  true,
 		Adapter:  "memory",
 		Interval: 60,
 		TTL:      16 * time.Hour,
 	},
 	LastCommit: struct {
-		Enabled      bool
 		TTL          time.Duration `ini:"ITEM_TTL"`
 		CommitsCount int64
 	}{
-		Enabled:      true,
 		TTL:          8760 * time.Hour,
 		CommitsCount: 1000,
 	},
@@ -65,30 +60,12 @@ func loadCacheFrom(rootCfg ConfigProvider) {
 		if CacheService.Conn == "" {
 			CacheService.Conn = "50000"
 		}
-	case "": // disable cache
-		CacheService.Enabled = false
 	default:
 		log.Fatal("Unknown cache adapter: %s", CacheService.Adapter)
 	}
 
-	if CacheService.Enabled {
-		log.Info("Cache Service Enabled")
-	} else {
-		log.Warn("Cache Service Disabled so that captcha disabled too")
-		// captcha depends on cache service
-		Service.EnableCaptcha = false
-	}
-
 	sec = rootCfg.Section("cache.last_commit")
-	if !CacheService.Enabled {
-		CacheService.LastCommit.Enabled = false
-	}
-
 	CacheService.LastCommit.CommitsCount = sec.Key("COMMITS_COUNT").MustInt64(1000)
-
-	if CacheService.LastCommit.Enabled {
-		log.Info("Last Commit Cache Service Enabled")
-	}
 }
 
 // TTLSeconds returns the TTLSeconds or unix timestamp for memcache