Revert "Read only the first line instead of loading the whole file"

This reverts commit a5b573eaaa.

The file shall always have one single line, no need to create a new method

app/src/main/java/com/topjohnwu/magisk/utils/Utils.java

@@ -75,17 +75,6 @@ public class Utils {
         return ret;
     }
 
-    public static String readFirstLine(String path) {
-        List<String> ret;
-        String command = "head -1 " + path;
-        if (Shell.rootAccess()) {
-            ret = Shell.su(command);
-        } else {
-            ret = Shell.sh(command);
-        }
-        return isValidShellResponse(ret) ? ret.get(0) : null;
-    }
-
     public static void dlAndReceive(Context context, DownloadReceiver receiver, String link, String filename) {
         if (isDownloading) {
             return;