How can I remove Skype 8's icon from the menu bar?
Since Skype 8 is an Electron app you can modify its source code. Run this command in Terminal:

LC_ALL=C sed -i '' -e "s/this._tray =/\\/\\/is._tray =/" -e "s/this._trayBaseToolTip =/return;\\/\\/yBaseToolTip =/" /Applications/Skype.app/Contents/Resources/app.asar


It will prevent the menu bar icon from being created.