remove fuchsia_entrypoint_shim directory (#63605)

packages/flutter_tools/fuchsia_entrypoint_shim/README.md

-This directory serves as a placeholder directory for the package roots of
-various fuchsia tools which use the flutter_tools library.
-
-This is required to provide a workaround for the fuchsia build system.
-When this directory is not present the various tools specified in the
-`dart_tool` directives in the flutter_tools/BUILD.gn file will end up
-having the same package root entry written in the .packages file. This
-causes the build to fail because the dart compiler has a requirement that
-libraries must have a unique package URI. By specifying a package root which
-is a subdirectory of this directory for these tools we avoid having the build
-system create duplicate package roots for the generated libraries for these
-tools.
-
-Note that we cannot move the location of the main files for these tools because
-the paths are hardcoded in the fuchsia tree.
-
-
-Tracking Bugs:
-- fxbug.dev/51373 (move flutter_tools/BUILD.gn to fuchsia repo)
-- fxbug.dev/51375 (do not refence fuchsia_tester.dart directly)
-- fxbug.dev/51375 (remove the fuchsia_entrypoint_shim directory)

packages/flutter_tools/fuchsia_entrypoint_shim/fuchsia_asset_builder/pubspec.yaml

-name: flutter_asset_builder
-description: Tools for building Flutter applications
-homepage: https://flutter.dev
-author: Flutter Authors <flutter-dev@googlegroups.com>
-
-environment:
-  # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.7.0 <3.0.0"
-
-dartdoc:
-  # Exclude this package from the hosted API docs.
-  nodoc: true
-
-# PUBSPEC CHECKSUM: 0000

packages/flutter_tools/fuchsia_entrypoint_shim/fuchsia_attach/pubspec.yaml

-name: flutter_attach
-description: Tools for building Flutter applications
-homepage: https://flutter.dev
-author: Flutter Authors <flutter-dev@googlegroups.com>
-
-environment:
-  # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.7.0 <3.0.0"
-
-dartdoc:
-  # Exclude this package from the hosted API docs.
-  nodoc: true
-
-# PUBSPEC CHECKSUM: 0000

packages/flutter_tools/fuchsia_entrypoint_shim/fuchsia_builder/pubspec.yaml

-name: flutter_builder
-description: Tools for building Flutter applications
-homepage: https://flutter.dev
-author: Flutter Authors <flutter-dev@googlegroups.com>
-
-environment:
-  # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.7.0 <3.0.0"
-
-dartdoc:
-  # Exclude this package from the hosted API docs.
-  nodoc: true
-
-# PUBSPEC CHECKSUM: 0000

packages/flutter_tools/fuchsia_entrypoint_shim/fuchsia_tester/pubspec.yaml

-name: flutter_tester
-description: Tools for building Flutter applications
-homepage: https://flutter.dev
-author: Flutter Authors <flutter-dev@googlegroups.com>
-
-environment:
-  # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.7.0 <3.0.0"
-
-dartdoc:
-  # Exclude this package from the hosted API docs.
-  nodoc: true
-
-# PUBSPEC CHECKSUM: 0000