Remove left over code from deprecating Android < 21 (#30243)

Summary:
Came to learn RN is deprecating Android 19, 20: https://github.com/facebook/react-native/commit/a17ff44adcf003dd4e4ef2301e1f80b77913f712

Did a quick check of left over code from the deprecation.

## Changelog

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https://github.com/facebook/react-native/wiki/Changelog
-->

[Android] [Deprecated] - Cleanup usages of deprecated Android API

Pull Request resolved: https://github.com/facebook/react-native/pull/30243

Reviewed By: fkgozali

Differential Revision: D24548084

Pulled By: JoshuaGross

fbshipit-source-id: 3054ca1455bcff2bd5c9791633942dc0cca7cb2c

ReactAndroid/src/main/java/com/facebook/react/bridge/queue/ReactQueueConfigurationSpec.java

@@ -19,8 +19,6 @@ import com.facebook.infer.annotation.Assertions;
  */
 public class ReactQueueConfigurationSpec {
 
-  private static final long LEGACY_STACK_SIZE_BYTES = 2000000;
-
   private final MessageQueueThreadSpec mNativeModulesQueueThreadSpec;
   private final MessageQueueThreadSpec mJSQueueThreadSpec;
 
@@ -44,11 +42,7 @@ public class ReactQueueConfigurationSpec {
   }
 
   public static ReactQueueConfigurationSpec createDefault() {
-    MessageQueueThreadSpec spec =
-        Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP
-            ? MessageQueueThreadSpec.newBackgroundThreadSpec(
-                "native_modules", LEGACY_STACK_SIZE_BYTES)
-            : MessageQueueThreadSpec.newBackgroundThreadSpec("native_modules");
+    MessageQueueThreadSpec spec = MessageQueueThreadSpec.newBackgroundThreadSpec("native_modules");
     return builder()
         .setJSQueueThreadSpec(MessageQueueThreadSpec.newBackgroundThreadSpec("js"))
         .setNativeModulesQueueThreadSpec(spec)