added a delete function to the canvases map when disposing of HTMLMesh (#24779)
added a delete function to the canvases map when disposing of HTMLMesh (#24779)

Co-authored-by: Jonathan Davidson <135b7423fa64234b1d91e1cfaefa8d559bc65177@canterbury.ac.nz>
WestLangley/three.js,mrdoob/three.js,06wj/three.js,WestLangley/three.js,06wj/three.js,mrdoob/three.js