Remove needless '&mut self' from HTMLButtonElementMethods.
Remove needless '&mut self' from HTMLCanvasElementMethods.
Remove needless '&mut self' from HTMLDataElementMethods.
Remove needless '&mut self' from HTMLDirectryElementMethods.
Remove needless '&mut self' from HTMLDivElementMethods.
Remove needless '&mut self' from HTMLDListElementMethods.
Remove needless '&mut self' from HTMLEmbedElementMethods.
Remove needless '&mut self' from HTMLFieldSetElementMethods.
Remove needless '&mut self' from HTMLFontElementMethods.
Remove needless '&mut self' from HTMLFormElementMethods.
Remove needless '&mut self' from HTMLFrameElementMethods.
Remove needless '&mut self' from HTMLFrameSetElementMethods.
Remove needless '&mut self' from HTMLHeadingElementMethods.
Remove needless '&mut self' from HTMLHRElementMethods.
Remove needless '&mut self' from HTMLLegendElementMethods.
Remove needless '&mut self' from HTMLLabelElementMethods.
Remove needless '&mut self' from HTMLInputElementMethods.
Remove needless '&mut self' from HTMLHtmlElementMethods.
Remove needless '&mut self' from HTMLLIElementMethods.
Remove needless '&mut self' from HTMLLinkElementMethods.