desktopToDarwinBundle: Fixup Exec

The "Exec" key in desktop items sometimes has one of the `%f`, `%F`,
`%u` and `%U` suffixes, which specify whether the command takes a file,
multiple files or a generalized URL or URLs. Darwin application bundles
do no understand this syntax so we do the next best thing, which is
simply dropping it.

pkgs/build-support/setup-hooks/desktop-to-darwin-bundle.sh

@@ -176,7 +176,7 @@ convertDesktopFile() {
     local -r file=$1
     local -r sharePath=$(dirname "$(dirname "$file")")
     local -r name=$(getDesktopParam "${file}" "^Name")
-    local -r exec=$(getDesktopParam "${file}" "Exec")
+    local -r exec=$(getDesktopParam "${file}" "Exec" | sed -e 's/ %[fFuU]$//')
     local -r iconName=$(getDesktopParam "${file}" "^Icon")
     local -r squircle=$(getDesktopParam "${file}" "X-macOS-SquircleIcon")