[PRQ#50924] Deletion Request for clang90

MarsSeed [1] filed a deletion request for clang90 [2]: This legacy clang version from 2019 is no longer needed by any build on AUR, and is safe to delete. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/clang90/