build(devshell): remove macOS brew and SHARE_PATH sed substitutions

- Remove sed expressions that replaced local SHARE_PATH and removed
Homebrew check
- Rely on existing darwin-specific substitutions and Nix-provided qemu
paths
- Simplify shellHook and avoid accidental replacements on non-Darwin
systems

Signed-off-by: Martin Wimpress <martin@wimpress.org>

Author: flexiondotorg

devshell.nix

@@ -58,8 +58,6 @@ mkShell {
           -e '/OVMF_CODE_4M.fd/s|ovmfs=(|ovmfs=("${OVMF.firmware}","${OVMF.variables}" |' \
         ''
       }${lib.optionalString stdenv.isDarwin ''
-        -e 's|local SHARE_PATH="/usr/share"|local SHARE_PATH="${pkgs.qemu_full}/share"|' \
-        -e '/command -v brew/,/^[[:space:]]*fi$/{ /command -v brew/s/.*/            : # Nix provides QEMU, skip brew check/; /SHARE_PATH.*brew/d; /^[[:space:]]*fi$/d; }' \
         -e 's|ovmfs=("[$][{]SHARE_PATH}/OVMF/OVMF_CODE_4M.secboot.fd"|ovmfs=("${pkgs.qemu_full}/share/qemu/edk2-x86_64-secure-code.fd","${pkgs.qemu_full}/share/qemu/edk2-i386-vars.fd" "''${SHARE_PATH}/OVMF/OVMF_CODE_4M.secboot.fd"|' \
         -e 's|ovmfs=("[$][{]SHARE_PATH}/OVMF/OVMF_CODE_4M.fd"|ovmfs=("${pkgs.qemu_full}/share/qemu/edk2-x86_64-code.fd","${pkgs.qemu_full}/share/qemu/edk2-i386-vars.fd" "''${SHARE_PATH}/OVMF/OVMF_CODE_4M.fd"|' \
         -e 's|ovmfs=("/usr/share/AAVMF/AAVMF_CODE.fd"|ovmfs=("${pkgs.qemu_full}/share/qemu/edk2-aarch64-code.fd","${pkgs.qemu_full}/share/qemu/edk2-arm-vars.fd" "/usr/share/AAVMF/AAVMF_CODE.fd"|' \