not necessary to add json in macro

src/kmailtransport/plugins/smtp/CMakeLists.txt

 if (BUILD_TESTING)
     add_subdirectory(autotests)
 endif()
-kcoreaddons_add_plugin(mailtransport_smtpplugin JSON smtpmailtransport.json INSTALL_NAMESPACE "kf${QT_MAJOR_VERSION}/mailtransport")
+kcoreaddons_add_plugin(mailtransport_smtpplugin INSTALL_NAMESPACE "kf${QT_MAJOR_VERSION}/mailtransport")
 
 target_sources(mailtransport_smtpplugin PRIVATE
     smtpmailtransportplugin.cpp

src/kmailtransportakonadi/plugins/CMakeLists.txt

-kcoreaddons_add_plugin(mailtransport_akonadiplugin JSON akonadimailtransport.json INSTALL_NAMESPACE "kf${QT_MAJOR_VERSION}/mailtransport")
+kcoreaddons_add_plugin(mailtransport_akonadiplugin INSTALL_NAMESPACE "kf${QT_MAJOR_VERSION}/mailtransport")
 target_sources(mailtransport_akonadiplugin PRIVATE
     akonadimailtransportplugin.cpp
     resourcesendjob.cpp