calprintdefaultplugins remove not used variable
Fix clazy issue "src/printing/calprintdefaultplugins.cpp:732:9: warning: unused QStringList [clazy-unused-non-trivial-variable]".
Fix clazy issue "src/printing/calprintdefaultplugins.cpp:732:9: warning: unused QStringList [clazy-unused-non-trivial-variable]".