docs: drop the GEOS 64 mains-clock claim

Author: kfox

docs/GEOS64_Usage.md

@@ -34,7 +34,6 @@
 * GEOS starts with the date and time of the TeensyROM's real-time clock, adjusted by the Time Zone setting.
   * Set the clock and time zone in the Settings menu (`F8`, page 6). See [General Usage](General_Usage.md#the-settings-menu).
   * Without Ethernet, the clock can also be set over USB with the `SetRTCToken` command. See [Remote Command Protocol](ControlComms.md).
-* GEOS's clock runs fast on a PAL C64 on 60 Hz mains, and slow on an NTSC C64 on 50 Hz mains. Stock GEOS does the same.
 
 ## Messages
 If GEOS 64 can't start, the TeensyROM stays at the menu and shows one of these: