wizard: do not force change of root password

We are forcing a change through the installer, which is where
the majority starts from.  We don't want to enforce a change
twice.

We can't really see if we installed or went through a factory
reset, so this is (was) the best of both worlds in conjunction
with the new installer feature.

While here, annotate that it is possible to leave it "empty".

This reverts commit 5eb2c986.

src/wizard/system.xml

@@ -545,6 +545,7 @@
 		<field>
 			<name>Admin Password</name>
 			<type>password</type>
+			<description>(leave empty to keep current one)</description>
 		</field>
 		<field>
 			<name>Admin Password AGAIN</name>
@@ -566,9 +567,6 @@
 			print_info_box("Passwords do not match! Please press back in your browser window and correct.");
 			die;
 		}
-	} else {
-		print_info_box("You must set a new password! Please press back in your browser window and correct.");
-		die;
 	}
 	</stepsubmitphpaction>
 </step>