Make getTurboModule required in RCTTurboModule protocol

Summary:
This change should make all type-safe NativeModules TurboModule-compatible.

Changelog: [Internal]

Differential Revision: D24729493

fbshipit-source-id: 7712708a24d675ca567225797016a7ff66a2920e

ReactCommon/react/nativemodule/core/platform/ios/RCTTurboModule.h

@@ -108,8 +108,6 @@ class JSI_EXPORT ObjCTurboModule : public TurboModule {
  */
 @property (nonatomic, weak) id<RCTTurboModuleRegistry> turboModuleRegistry;
 
-@optional
-// This should be required, after migration is done.
 - (std::shared_ptr<facebook::react::TurboModule>)getTurboModule:
     (const facebook::react::ObjCTurboModule::InitParams &)params;