Remove old AST factory constructors from analyzer.

This reapplies the remainder of
1d028eed8d (which was reverted due to
conflicts with dev_compiler), since dev_compiler has now been fixed to
use analyzer's new astFactory.

R=brianwilkerson@google.com, scheglov@google.com

Review URL: https://codereview.chromium.org/2549613002 .

pkg/analyzer/CHANGELOG.md

@@ -2,6 +2,7 @@
 * Changed the API for creating BazelWorkspace.  It should now be constructed using BazelWorkspace.find().  Note that this might return `null` in the event that the given path is not part of a BazelWorkspace.
 * Added an AST structure to support asserts in constructor initializers (AssertInitializer).  AstVisitor classes must now implement visitAssertInitializer().
 * Changed the API for creating PartOfDirective.  It now accepts a StringLiteral URI, to accomodate "part of" declarations with a URI string rather than a library name.
+* Removed AST constructors.  AST nodes should now be created using `astFactory`, located in `package:analyzer/dart/ast/standard_ast_factory.dart`.
 
 ## 0.29.0-alpha.0
 * Removed `Element.docRange`.