Remove unneeded project(kirigami) in src/CMakeList.txt
Resets all the PROJECT_* variables, which is not made use of and might be unexpected compared to other KF modules
Also currently will trigger a build fail once KF_DEP_VERSION is set to 5.83 later this release cycle, as ecm_generate_pri_file() then will rely on PROJECT_STRING only instead of PROJECT_STRING_VERSION (deprecated variable only set by ecm_setup_version()), but project(kirigami) will unset PROJECT_STRING to empty string and thus ecm_generate_pri_file() throw up. Other option would be to use new VERSION argument with ecm_generate_pri_file() instead of magic by context variables, but that would be inconsistent with the other KF modules, so for now I go with consistency.