fix: incorrect O_DIRECT behavior for reads (#12811)

O_DIRECT behavior was broken and it was still
caching all the reads, this change properly fixes
this behavior.

internal/config/storageclass/help.go

@@ -34,12 +34,6 @@ var (
 			Optional:    true,
 			Type:        "string",
 		},
-		config.HelpKV{
-			Key:         ClassDMA,
-			Description: `enable O_DIRECT for both read and write, defaults to "write" e.g. "read+write"`,
-			Optional:    true,
-			Type:        "string",
-		},
 		config.HelpKV{
 			Key:         config.Comment,
 			Description: config.DefaultComment,