Reduce cmake variable

messagecomposer/src/imagescaling/tests/CMakeLists.txt

-set(imagescaling_gui_SRCS imagescaling_gui.cpp)
-add_executable(imagescaling_gui ${imagescaling_gui_SRCS})
+add_executable(imagescaling_gui imagescaling_gui.cpp)
 target_link_libraries(imagescaling_gui
   KF5::KIOCore
   KF5::MessageComposer

messagecomposer/src/statusbarwidget/autotests/CMakeLists.txt

 
-set( kmail_statusbarlabeltoggledstate_source statusbarlabeltoggledstatetest.cpp)
-add_executable(statusbarlabeltoggledstatetest ${kmail_statusbarlabeltoggledstate_source})
+add_executable(statusbarlabeltoggledstatetest statusbarlabeltoggledstatetest.cpp)
 ecm_mark_as_test(kmail-statusbarlabeltoggledstatetest)
 target_link_libraries( statusbarlabeltoggledstatetest Qt::Test KF5::KIOWidgets KF5::I18n KF5::MessageComposer)