Mark deprecated API in FlutterDartProject.h as unavailable (#4552)

shell/platform/darwin/ios/framework/Headers/Flutter.h

@@ -8,10 +8,15 @@
 /**
  BREAKING CHANGES:
 
- January 09, 2018: Deprecated FlutterStandardBigInteger and its use in
- FlutterStandardMessageCodec and FlutterStandardMethodCodec. Scheduled to
+ January 15, 2018: Marked "initWithFLXArchive" and
+ "initWithFLXArchiveWithScriptSnapshot" as unavailable following the
+ deprecation from December 11, 2017. Scheduled to be removed on February
+ 19, 2018.
+
+ January 09, 2018: Deprecated "FlutterStandardBigInteger" and its use in
+ "FlutterStandardMessageCodec" and "FlutterStandardMethodCodec". Scheduled to
  be marked as unavailable once the deprecation has been available on the
- flutter/flutter alpha branch for four weeks. FlutterStandardBigInteger was
+ flutter/flutter alpha branch for four weeks. "FlutterStandardBigInteger" was
  needed because the Dart 1.0 int type had no size limit. With Dart 2.0, the
  int type is a fixed-size, 64-bit signed integer. If you need to communicate
  larger integers, use NSString encoding instead.

shell/platform/darwin/ios/framework/Headers/FlutterDartProject.h

@@ -17,14 +17,14 @@ FLUTTER_EXPORT
 - (instancetype)initWithFLXArchive:(NSURL*)archiveURL
                           dartMain:(NSURL*)dartMainURL
                           packages:(NSURL*)dartPackages NS_DESIGNATED_INITIALIZER
-    FLUTTER_DEPRECATED(
-        "This initializer is no longer used since the FLX will be deprecated. "
-        "Instead, use [initWithFlutterAssets].");
+    FLUTTER_UNAVAILABLE(
+        "This initializer is no longer available. See the deprecation message from "
+        "December 11, 2017 in Flutter.h. Instead, use [initWithFlutterAssets].");
 
 - (instancetype)initWithFLXArchiveWithScriptSnapshot:(NSURL*)archiveURL NS_DESIGNATED_INITIALIZER
-    FLUTTER_DEPRECATED(
-        "This initializer is no longer used since the FLX will be deprecated. "
-        "Instead, use [initWithFlutterAssetsWithScriptSnapshot].");
+    FLUTTER_UNAVAILABLE(
+        "This initializer is no longer available. See the deprecation message from "
+        "December 11, 2017 in Flutter.h. Instead, use [initWithFlutterAssetsWithScriptSnapshot].");
 
 - (instancetype)initWithFlutterAssets:(NSURL*)flutterAssetsURL
                              dartMain:(NSURL*)dartMainURL