SVG tref element used in WPT tests needs to be removed.

[karlcow]

These are currently using tref

conformance-checkers/html-svg/styling-pres-02-f-novalid.html
conformance-checkers/html-svg/text-align-04-b-isvalid.html
conformance-checkers/html-svg/text-tref-01-b-isvalid.html
html/editing/dnd/svg/004.svg
html/editing/dnd/svg/009.svg
html/editing/dnd/svg/047.svg
html/editing/dnd/svg/048.svg
svg/import/styling-pres-02-f-manual.svg
svg/import/text-align-04-b-manual.svg
svg/import/text-tref-01-b-manual.svg
svg/import/text-tref-02-b-manual.svg
svg/import/text-tref-03-b-manual.svg

tref has been removed from SVG2 for a while already.
https://w3c.github.io/svgwg/svg2-draft/changes.html#:~:text=Removed%20the%20'tref'%20element.