Switch to pure sh

This required manual conflict resolution. In addition to
removing external commands, part of the `with-overclocking`
functionality was removed (the overclocking part).

check-overscan

@@ -1,9 +1,17 @@
 #!/bin/sh
 
 configFile="/boot/firmware/config.txt";
+found=;
 
-if [ ! $(awk '/disable_overscan=1/ { print("1") }' $configFile) ]; then
-    echo "
+while IFS= read -r line || [ -n "$line" ]; do
+    if [ "$line" = "disable_overscan=1" ]; then
+        found="1";
+    fi;
+done < $configFile;
+
+if [ ! $found ]; then
+    printf "
 # Remove black borders
-disable_overscan=1" >> $configFile;
+disable_overscan=1
+" >> $configFile;
 fi;