MAIL_URL was overriden with database info all the time.
Now if MAIL_URL exists is not overwritten and if neither MAIL_URL nor
exists valid admin panel data MAIL_URL is not set.
MAIL_FROM was ignored. Same behaviour, env variable has bigger priority
than database configuration.
On both cases, althrought environment variable is set, updating admin-panel
mail settings will load new info and ignore the environment variable.
Remove some code that is not needed anymore