kconf_update: Allow repeated tests in --testmode by ignoring kconf_updaterc

https://techbase.kde.org/Development/Tools/Using_kconf_update#Debugging_and_testing describes how to run repeated tests of kconf_update scripts in --testmode. It is necessary to delete update group flags from kconf_updaterc, which is inconvenient.

With this patch, kconf_update will not use kconf_updaterc when in --testmode, so this step is no longer necessary.

Additionally, running all installed update scripts automatically is no longer possible in --testmode, since that is probably only useful if you have your home directory in ~/.qttest/config/.

I don’t expect problems, since this affects only --testmode, and the update group flags are still present in the modified config files themselves.