How to completely remove an Apple Watch from your iPhone/iCloud account
If you wish to sell your Watch on (or simply don't have it anymore), you need to follow these steps specifically in this order or the new user will find it's still tied to you (for some reason, Apple has made this extremely tortuous and unintuitive when they could have made it a single toggle switch in settings somewhere):
Go to iPhone → Watch.app → "Unpair Watch"
Apple Watch → "Erase All Content and Settings" → now power it OFF
iCloud on laptop/desktop → Find iPhone → click on 'All Devices' & select your watch → "Remove from Account"
^^^Ridiculous "all around the houses" approach for what should be much simpler, but that's Apple for you since Mr Jobs died :(
FYI: Powering the Watch OFF at end of step 2 ensures it isn't connected to iCloud which gives the Remove option in step 3
