Strip unused attributes

[eelcoj]

<%= icon "arrows-clockwise" %>

Currently renders:

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256" stroke-width="" data="" class=""><rect width="256" height="256" fill="none"></rect><polyline points="168 96 216 96 216 48" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="16"></polyline><path d="M216,96,187.72,67.72A88,88,0,0,0,64,67" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="16"></path><polyline points="88 160 40 160 40 208" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="16"></polyline><path d="M40,160l28.28,28.28A88,88,0,0,0,192,189" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="16"></path></svg>

Notice the empty: stroke-width="" data="" class=""