The Windows\Linux keyboard shortcut for removing trailing spaces in VS Code is:

Ctrl + K Ctrl + X

On macOS it is:

⌘ + K ⌘ + X

Alternatively you can access the option via the Command Palette. (Windows\Linux: Ctrl+Shift+P macOS: ⇧⌘P, F1) and type trim which will shorten the options, select the command “Trim Trailing Whitespace”