Remove unneeded SRCS variables

src/applet/plugin/CMakeLists.txt

-set(bluetoothplugin_SRCS
+add_library(bluetoothplugin SHARED
     devicesproxymodel.cpp
     launchapp.cpp
     notify.cpp
     bluetoothplugin.cpp)
 
-add_library(bluetoothplugin SHARED ${bluetoothplugin_SRCS})
 target_link_libraries(bluetoothplugin
     Qt5::Core
     Qt5::Qml

src/kcm/CMakeLists.txt

-set(kcmbluetooth_SRCS bluetooth.cpp)
+add_library(kcm_bluetooth MODULE bluetooth.cpp)
 
-kconfig_add_kcfg_files(kcmbluetooth_SRCS GENERATE_MOC
+kconfig_add_kcfg_files(kcm_bluetooth GENERATE_MOC
                     ../settings/filereceiversettings.kcfgc)
 
-add_library(kcm_bluetooth MODULE ${kcmbluetooth_SRCS})
-
 target_link_libraries(kcm_bluetooth
     Qt5::Gui
     Qt5::Qml