Revert commits that set API key via parameter instead of config.

This reverts commits 84afda30a0b3166a8beafd8b1d949fc7bd8bd418 and
d81af707ecc4d9bb640e4b6d55fcc4b7bd9b9c3a.
Start syncthing with STNORESTART flag.

This avoids the problem where an occupied GUI start lets syncthing-android
start, but API calls fail silently.