Remove Mixin version checker.

src/main/java/io/github/zekerzhayard/optiforge/asm/fml/OptiForgeWrapperTransformationService.java

@@ -91,7 +91,7 @@ public void initialize(@Nonnull IEnvironment environment) {
             // We should check if it is under development environments or loaded required versions successfully.
             if (checked = Files.isDirectory(path) || currentFMLVersion.length() == 0) {
                 // Nothing to do.
-            } else if (checked = VersionChecker.IS_LOADED && VersionChecker.checkOptiFineVersion(VersionChecker.DEFAULT_FUNCTION, true) && VersionChecker.checkMixinVersion(VersionChecker.DEFAULT_FUNCTION) && VersionChecker.checkForgeVersion(VersionChecker.DEFAULT_FUNCTION, currentFMLVersion.toString())) {
+            } else if (checked = VersionChecker.IS_LOADED && VersionChecker.checkOptiFineVersion(VersionChecker.DEFAULT_FUNCTION, true) && VersionChecker.checkForgeVersion(VersionChecker.DEFAULT_FUNCTION, currentFMLVersion.toString())) {
                 // FML can't detect IModLocator when ITransformationService exists in the same jar, so we must add it manually.
                 ModDirTransformerDiscoverer.getExtraLocators().add(path);
             } else {

src/main/java/io/github/zekerzhayard/optiforge/asm/fml/VersionChecker.java

@@ -181,27 +181,6 @@ public static String getOptiFineVersionFromJar(Path optifine) {
         return null;
     }
 
-    /**
-     * Mixin has it own version checker system, so this method only check if Mixin exists.
-     */
-    public static boolean checkMixinVersion(Function<String, Boolean> function) {
-        try {
-            Class.forName("org.spongepowered.asm.launch.MixinBootstrap").getField("VERSION");
-        } catch (Exception e) {
-            StringBuilder message = new StringBuilder(
-                "It looks like you have not install Mixin, you can download it from https://www.curseforge.com/minecraft/mc-mods/mixinbootstrap.\n" +
-                "The game will continue, and run without OptiFine and OptiForge.\n\n" +
-                e + "\n"
-            );
-            for (StackTraceElement traceElement : e.getStackTrace()) {
-                message.append("\tat ").append(traceElement).append("\n");
-            }
-            LOGGER.error(message.toString());
-            return function.apply(message.toString());
-        }
-        return true;
-    }
-
     /**
      * FML can't check the build number and if can't match minor version, game won't crash or prompt players prompts
      */