rm CODEOWNERS (#1399)

Versus #1367 which approved this in principle, this is the actual removal (I've updated write permissions in GH now).

CODEOWNERS

@@ -1,23 +0,0 @@
-# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-# Exceptions. See /LICENSE for license information.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-# Most of the repository consists of implementation code or other supporting
-# material for the implementation of Carbon. Rather than enumerate these, we
-# default them to implementation team ownership, which will be overridden by
-# later lines.
-*                   @carbon-language/implementation-team
-/*                  @carbon-language/implementation-team
-
-# Carbon leads own the core language and project documentation. The
-# implementation team has access for small (non-evolution) edits.
-/*.md               @carbon-language/carbon-leads @carbon-language/implementation-team
-/docs/              @carbon-language/carbon-leads @carbon-language/implementation-team
-
-# Carbon leads should review proposals and license changes.
-/proposals/         @carbon-language/carbon-leads
-/LICENSE            @carbon-language/carbon-leads
-
-# Carbon leads own ACLs. This is last to prevent other rules from accidentally
-# overriding it.
-CODEOWNERS          @carbon-language/carbon-leads