Remove feature specs for merged standard

The ECMA committee merged the feature PRs for "async streams" and "null-coalescing assignment" at the June 11 meeting. It's time to unpublish those feature specifications.

Author: BillWagner

docfx.json

@@ -81,6 +81,8 @@
                     "csharp-8.0/nullable-reference-types-specification.md",
                     "csharp-8.0/nested-stackalloc.md",
                     "csharp-8.0/readonly-instance-members.md",
+                    "csharp-8.0/null-coalescing-assignment.md",
+                    "csharp-8.0/async-streams.md",
                     "csharp-9.0/nullable-reference-types-specification.md",
                     "csharp-9.0/nullable-constructor-analysis.md",
                     "csharp-9.0/nullable-parameter-default-value-analysis.md",
@@ -618,10 +620,8 @@
                 "_csharpstandard/standard/Bibliography.md": "Bibliography",
                 "_csharplang/proposals/csharp-8.0/patterns.md": "Recursive pattern matching",
                 "_csharplang/proposals/csharp-8.0/default-interface-methods.md": "Default interface methods",
-                "_csharplang/proposals/csharp-8.0/async-streams.md": "Async streams",
                 "_csharplang/proposals/csharp-8.0/ranges.md": "Ranges and indices",
                 "_csharplang/proposals/csharp-8.0/using.md": "Pattern based using and using declarations",
-                "_csharplang/proposals/csharp-8.0/null-coalescing-assignment.md": "Null coalescing assignment",
                 "_csharplang/proposals/csharp-9.0/covariant-returns.md": "Covariant return types",
                 "_csharplang/proposals/csharp-9.0/extending-partial-methods.md": "Extending partial methods",
                 "_csharplang/proposals/csharp-9.0/extension-getenumerator.md": "Extension GetEnumerator support in foreach",
@@ -744,10 +744,8 @@
                 "_csharpstandard/standard/Bibliography.md": "This appendix lists external standards referenced in this specification.",
                 "_csharplang/proposals/csharp-8.0/patterns.md": "This feature specification describes recursive pattern matching, where patterns can nest inside other patterns.",
                 "_csharplang/proposals/csharp-8.0/default-interface-methods.md": "This feature specification describe the syntax updates necessary to support default interface methods. This includes declaring bodies in interface declarations, and supporting modifiers on declarations.",
-                "_csharplang/proposals/csharp-8.0/async-streams.md": "This feature specification describes async streams, which return streams of data asynchronously, typically as each element is produced or available.",
                 "_csharplang/proposals/csharp-8.0/ranges.md": "This feature specification describes the syntax for ranges and indices, which support indexing individual elements of a sequence or a range of a sequence from the start or end of that sequence.",
                 "_csharplang/proposals/csharp-8.0/using.md": "This feature specification supports pattern based using and using declarations to simplify resource cleanup.",
-                "_csharplang/proposals/csharp-8.0/null-coalescing-assignment.md": "This feature specification describes the syntax to support null coalescing assignment expressions using the '??=' operator.",
                 "_csharplang/proposals/csharp-9.0/covariant-returns.md": "This feature specification describes covariant return types, where overriding member declarations can return a type derived from the overridden member declaration.",
                 "_csharplang/proposals/csharp-9.0/extending-partial-methods.md": "This feature specification describes extensions to partial methods. These extensions enable source generators to create or call partial methods.",
                 "_csharplang/proposals/csharp-9.0/extension-getenumerator.md": "This feature specification describes the necessary pattern for an extension method to provide the GetEnumerator support in a foreach loop.",

docs/csharp/specification/toc.yml

@@ -135,8 +135,6 @@ items:
     items:
     - name: Ranges
       href: ../../../_csharplang/proposals/csharp-8.0/ranges.md
-    - name: Null coalescing assignment
-      href: ../../../_csharplang/proposals/csharp-8.0/null-coalescing-assignment.md
     - name: Target-typed new expressions
       href: ../../../_csharplang/proposals/csharp-9.0/target-typed-new.md
     - name: Target-typed conditional expression
@@ -187,8 +185,6 @@ items:
       href: ../../../_csharplang/proposals/csharp-9.0/local-function-attributes.md
     - name: Pattern based using and using declarations
       href: ../../../_csharplang/proposals/csharp-8.0/using.md
-    - name: Async streams
-      href: ../../../_csharplang/proposals/csharp-8.0/async-streams.md
     - name: Lock object semantics
       href: ../../../_csharplang/proposals/csharp-13.0/lock-object.md
     - name: Allow `ref` and `unsafe`