Simplify check_required_binaries function

Don't surround variables with quotes, they're not necessary in Bash.

optipdf

@@ -27,7 +27,7 @@ Optimize PDF files for size.
   --no-preserve-timestamp  Omit timestamp from original file (default).
   --                Terminate options list.
 
-Copyright (C) 2021-2022 Dan Church.
+Copyright (C) 2021-2024 Dan Church.
 License GPLv3: GNU GPL version 3.0 (https://www.gnu.org/licenses/gpl-3.0.html)
 with Commons Clause 1.0 (https://commonsclause.com/).
 This is free software: you are free to change and redistribute it.
@@ -47,7 +47,7 @@ NO_MORE_FLAGS=0
 for ARG; do
     # Assume arguments that don't begin with a - are supposed to be files or other operands
     if [[ $NO_MORE_FLAGS -eq 0 && $ARG = -* ]]; then
-        case "$ARG" in
+        case $ARG in
             --backup=*)
                 KEEP_BACKUP_SUFFIX=${ARG#*=}
                 ;;
@@ -114,9 +114,7 @@ check_required_binaries() {
     done
     if [[ ${#MISSING[@]} -gt 0 ]]; then
         printf 'Error: You are missing required programs:\n' >&2
-        for BIN in "${MISSING[@]}"; do
-            printf -- '- %s\n' "$BIN" >&2
-        done
+        printf -- '- %s\n' "${MISSING[@]}" >&2
         exit 2
     fi
 }