Add rules.mk cleaning script

util/rules_cleaner.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+
+# This script finds all rules.mk files in keyboards/ subdirectories,
+# and deletes the build option filesize impacts from them.
+
+# Print an error message with the word "ERROR" in red.
+echo_error() {
+    echo -e "[\033[0;91mERROR\033[m]: $1"
+}
+
+# If we've been started from util/, we want to be in qmk_firmware/
+[[ "$PWD" == *util ]] && cd ..
+
+# The root qmk_firmware/ directory should have a subdirectory called quantum/
+if [ ! -d "quantum" ]; then
+    echo_error "Could not detect the QMK firmware directory!"
+    echo_error "Are you sure you're in the right place?"
+    exit 1
+fi
+
+# Set the inplace editing parameter for sed.
+# macOS/BSD sed expects a file extension immediately following -i.
+set_sed_i() {
+    sed_i=(-i)
+
+    case $(uname -a) in
+        *Darwin*) sed_i=(-i "")
+    esac
+}
+
+set_sed_i
+find keyboards -type f -name 'rules.mk' -exec sed "${sed_i[@]}" -e "s/(.*)$/""/g" {} +
+
+echo "Cleaned up rules.mk files."