Remove height auto rule for SVG logo

Follow-up from #3026851-3: Support multilingual SVG logos for branding block

Additional testing around this revealed that `height: auto` CSS rule coming from bs_bootstrap/sass/components/partials/_navigation.scss:

// Inline SVG logo.
.site-logo-link--svg {
  svg {
    // SVG logo should respect parent dimension.
    max-width: 100%;
    height: auto;
  }
}

Is causing problems in IE11 and also it seems that this rule is not needed for other browsers.

Let us remove `height: auto;` line and add into documentation that for SVG logo version you must use width and height attributes in SVG tag if you want to support IE11.