removing unreachable codes in `gbackend`

modules/gapi/src/api/gbackend.cpp

@@ -36,7 +36,6 @@ cv::gapi::GBackend::Priv::compile(const ade::Graph&,
 {
     // ...and this method is here for the same reason!
     GAPI_Error("InternalError");
-    return {};
 }
 
 std::unique_ptr<cv::gimpl::GIslandExecutable>
@@ -224,7 +223,6 @@ void bindOutArg(Mag& mag, const RcDesc &rc, const GRunArgP &arg, HandleRMat hand
 
     default:
         util::throw_error(std::logic_error("Unsupported GShape type"));
-        break;
     }
 }
 
@@ -256,7 +254,6 @@ void resetInternalData(Mag& mag, const Data &d)
 
     default:
         util::throw_error(std::logic_error("Unsupported GShape type"));
-        break;
     }
 }
 
@@ -284,7 +281,6 @@ cv::GRunArg getArg(const Mag& mag, const RcDesc &ref)
                        mag.meta<cv::MediaFrame>().at(ref.id));
     default:
         util::throw_error(std::logic_error("Unsupported GShape type"));
-        break;
     }
 }
 
@@ -327,7 +323,6 @@ cv::GRunArgP getObjPtr(Mag& mag, const RcDesc &rc, bool is_umat)
 
     default:
         util::throw_error(std::logic_error("Unsupported GShape type"));
-        break;
     }
 }
 
@@ -359,7 +354,6 @@ void writeBack(const Mag& mag, const RcDesc &rc, GRunArgP &g_arg)
 
     default:
         util::throw_error(std::logic_error("Unsupported GShape type"));
-        break;
     }
 }