chore: drop the unused Noto Sans variable fonts (#29723)

The four Noto Sans variable fonts under open_webui/static/fonts have never been loaded. Removing them makes an installed package 40 MB smaller on disk, the wheel about 24 MB, and the Docker image about 80 MB, because the image currently stores the static directory twice.

The PDF generator registers only the static faces through add_font, and the stylesheet that names the variable fonts, pdf-style.css, is read into a variable that nothing ever uses, so no code path can reach them. The frontend never fetches these files either.

Only the four @font-face blocks that pointed at the deleted files are removed; the rest of the stylesheet, font stack included, is left exactly as it is.

The files were reachable under the public /static mount, so anything outside this repository that hotlinked them gets a 404 from now on.

Part of #29721.

backend/open_webui/static/assets/pdf-style.css

@@ -1,24 +1,4 @@
 /* HTML and Body */
-@font-face {
-	font-family: 'NotoSans';
-	src: url('fonts/NotoSans-Variable.ttf');
-}
-
-@font-face {
-	font-family: 'NotoSansJP';
-	src: url('fonts/NotoSansJP-Variable.ttf');
-}
-
-@font-face {
-	font-family: 'NotoSansKR';
-	src: url('fonts/NotoSansKR-Variable.ttf');
-}
-
-@font-face {
-	font-family: 'NotoSansSC';
-	src: url('fonts/NotoSansSC-Variable.ttf');
-}
-
 @font-face {
 	font-family: 'NotoSansSC-Regular';
 	src: url('fonts/NotoSansSC-Regular.ttf');