fix: include all public headers unconditionally in umbrella header (#595)

Co-authored-by: Mike Fullerton <mike@mikefullerton.com>
Co-authored-by: Worthing <115107835+w-goog@users.noreply.github.com>

Author: mikefullerton

GoogleSignIn/Sources/Public/GoogleSignIn/GoogleSignIn.h

@@ -13,11 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-#import <TargetConditionals.h>
-
-#if TARGET_OS_IOS && !TARGET_OS_MACCATALYST
 #import "GIDAppCheckError.h"
-#endif
 #import "GIDConfiguration.h"
 #import "GIDGoogleUser.h"
 #import "GIDProfileData.h"