Remove dead RCTEnableImageStoreManagerStorageQueue declaration

Summary:
`RCTImageStoreManager.h` declared `RCT_EXTERN void RCTEnableImageStoreManagerStorageQueue(BOOL enabled);`, but no definition exists anywhere in the tree and nothing calls it. A declared-but-never-defined external function is uncallable (any use would be a link error), so this is unreachable dead code.

Changelog: [Internal]

Differential Revision: D108012909

Author: sammy-SC

packages/react-native/Libraries/Image/RCTImageStoreManager.h

@@ -11,8 +11,6 @@
 #import <React/RCTBridgeProxy.h>
 #import <React/RCTURLRequestHandler.h>
 
-RCT_EXTERN void RCTEnableImageStoreManagerStorageQueue(BOOL enabled);
-
 @interface RCTImageStoreManager : NSObject <RCTURLRequestHandler>
 
 /**