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.

docs/content/administration/config-cheat-sheet.en-us.md

@@ -763,7 +763,6 @@ and
 
 ## Cache (`cache`)
 
-- `ENABLED`: **true**: Enable the cache.
 - `ADAPTER`: **memory**: Cache engine adapter, either `memory`, `redis`, `redis-cluster`, `twoqueue` or `memcache`. (`twoqueue` represents a size limited LRU cache.)
 - `INTERVAL`: **60**: Garbage Collection interval (sec), for memory and twoqueue cache only.
 - `HOST`: **_empty_**: Connection string for `redis`, `redis-cluster` and `memcache`. For `twoqueue` sets configuration for the queue.
@@ -775,7 +774,6 @@ and
 
 ## Cache - LastCommitCache settings (`cache.last_commit`)
 
-- `ENABLED`: **true**: Enable the cache.
 - `ITEM_TTL`: **8760h**: Time to keep items in cache if not used, Setting it to -1 disables caching.
 - `COMMITS_COUNT`: **1000**: Only enable the cache when repository's commits count great than.
 

docs/content/administration/config-cheat-sheet.zh-cn.md

@@ -721,7 +721,6 @@ Gitea 创建以下非唯一队列：
 
 ## 缓存 (`cache`)
 
-- `ENABLED`: **true**: 是否启用缓存。
 - `ADAPTER`: **memory**: 缓存引擎，可以为 `memory`, `redis`, `redis-cluster`, `twoqueue` 和 `memcache`. (`twoqueue` 代表缓冲区固定的LRU缓存)
 - `INTERVAL`: **60**: 垃圾回收间隔(秒)，只对`memory`和`towqueue`有效。
 - `HOST`: **_empty_**: 缓存配置。`redis`, `redis-cluster`，`memcache`配置连接字符串;`twoqueue` 设置队列参数
@@ -733,7 +732,6 @@ Gitea 创建以下非唯一队列：
 
 ### 缓存 - 最后提交缓存设置 (`cache.last_commit`)
 
-- `ENABLED`: **true**：是否启用缓存。
 - `ITEM_TTL`: **8760h**：如果未使用，保持缓存中的项目的时间，将其设置为 -1 会禁用缓存。
 - `COMMITS_COUNT`: **1000**：仅在存储库的提交计数大于时启用缓存。