[PRQ#50926] Deletion Request for llvm90

MarsSeed [1] filed a deletion request for llvm90 [2]: Cleanup of unneeded, broken legacy llvm 9.0 version from 2019. No longer needed by any other builds on AUR, except its defunct companions pending deletion: - clang90 (PRQ#50924) - compiler-rt90 (PRQ#50925) [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/llvm90/