chore: clean up the logic of greeter and lockscreen - #735

Include file: "seat/helper.h" not found.

Include file: "greeter/usermodel.h" not found.

Include file: "greeter/sessionmodel.h" not found.

Include file: <memory> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <map> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <wsessionlock.h> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: "greeter/greeterproxy.h" not found.

Include file: "common/treelandlogging.h" not found.

Include file: "utils/cmdline.h" not found.