Deprecate and remove in-memory object caching (#5481)

in-memory caching cannot be cleanly implemented
without the access to GC which Go doesn't naturally
provide. At times we have seen that object caching
is more of an hindrance rather than a boon for
our use cases.

Removing it completely from our implementation
  related to #5160 and #5182

docs/caching/README.md

@@ -1,27 +0,0 @@
-## Object Caching
-
-Object caching is on by default with following settings
-
- - Cache size is 50% of your RAM size. Caching is disabled
-   if your RAM size is smaller than 8GB.
-
- - Expiration of each entries happen on every 72 hours.
-
- - Garbage collection sweep of the expired entries happen every
-   1/4th the set expiration hours value (every 18 hours).
-
-NOTE: None of the settings can be configured manually.
-
-### Behavior
-
-Caching happens on both GET and PUT operations.
-
-- GET caches new objects for entries not found in cache.
-  Otherwise serves from the cache.
-
-- PUT/POST caches all successfully uploaded objects. Replaces
-  existing cached entry for the same object if needed.
-
-NOTE: Expiration happens automatically based on the configured
-interval as explained above, frequently accessed objects stay
-alive in cache for a significantly longer time on every cache hit.