[iOS] Remove a redundant detachHandlerWithTag definition (#4132)

## Description

Removes redundant `detachHandlerWithTag` definition, which was never
used and never implemented. Most likely a result of a merge commit.

## Test plan

Compile the app

Author: j-piasecki

packages/react-native-gesture-handler/apple/RNGestureHandlerRegistry.h

@@ -16,7 +16,6 @@
                       toView:(nonnull RNGHUIView *)view
               withActionType:(RNGestureHandlerActionType)actionType
             withHostDetector:(nullable RNGHUIView *)hostDetector;
-- (void)detachHandlerWithTag:(nonnull NSNumber *)handlerTag;
 - (void)detachHandlerWithTag:(nonnull NSNumber *)handlerTag fromHostDetector:(nonnull RNGHUIView *)hostDetectorView;
 - (void)dropHandlerWithTag:(nonnull NSNumber *)handlerTag;
 - (void)dropAllHandlers;