Remove airootfs files that conflict with package installs

These files exist in the airootfs overlay but are owned by packages
in packages.x86_64, causing 'exists in filesystem' errors during
mkarchiso pacman install:

- usr/lib/os-release (filesystem)
- usr/share/pacman/keyrings/cachyos-* (cachyos-keyring)
- etc/clamav/certs/clamav.crt (clamav)
- etc/skel/.zshrc (grml-zsh-config)

airootfs/usr/lib/os-release

@@ -1,12 +0,0 @@
-NAME="Alvin Arch Linux"
-PRETTY_NAME="Arch Linux"
-ID_LIKE=arch
-ID=arch
-BUILD_ID=rolling
-ANSI_COLOR="38;2;23;147;209"
-HOME_URL="https://archlinux.org/"
-DOCUMENTATION_URL="https://wiki.archlinux.org/"
-SUPPORT_URL="https://bbs.archlinux.org/"
-BUG_REPORT_URL="https://gitlab.archlinux.org/groups/archlinux/-/issues"
-PRIVACY_POLICY_URL="https://terms.archlinux.org/docs/privacy-policy/"
-LOGO=archlinux-logo