kconfig: qconf: remove initial call to conf_changed()

If any CONFIG option is changed while loading the .config file,
conf_read() calls conf_set_changed(true) and then the conf_changed()
callback.

With conf_read() moved after window initialization, the explicit
conf_changed() call can be removed.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>