[dart] Remove old dio generator (to be replaced with dart-dio-next) (#12109)

* remove old `dart-dio` generator which will be replaced by `dart-dio-next` in a seperate PR
* remove left-over `DartJaguarClinetCodegen` class which was sunset a while ago and is unused

.github/workflows/samples-dart.yaml

@@ -13,41 +13,8 @@ on:
       - 'samples/openapi3/client/petstore/dart*/**'
 
 jobs:
-  tests-dart-2-10:
-    name: Tests Dart 2.10
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-java@v3
-        with:
-          distribution: 'temurin'
-          java-version: 8
-      - name: Cache maven dependencies
-        uses: actions/cache@v3
-        env:
-          cache-name: maven-repository
-        with:
-          path: |
-            ~/.m2/repository
-            ~/.gradle
-          key: ${{ runner.os }}-${{ github.job }}-${{ env.cache-name }}-${{ hashFiles('**/pom.xml') }}
-      - name: Cache test dependencies
-        uses: actions/cache@v3
-        env:
-          cache-name: pub-cache
-        with:
-          path: $PUB_CACHE
-          key: ${{ runner.os }}-${{ github.job }}-${{ env.cache-name }}-${{ hashFiles('samples/**/pubspec.yaml') }}
-      - uses: dart-lang/setup-dart@v1
-        with:
-          sdk: 2.10.5
-      - name: Run tests
-        uses: ./.github/actions/run-samples
-        with:
-          name: samples.dart-2.10
-
-  tests-dart-2-13:
-    name: Tests Dart 2.13
+  tests-dart:
+    name: Tests Dart
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
@@ -77,4 +44,4 @@ jobs:
       - name: Run tests
         uses: ./.github/actions/run-samples
         with:
-          name: samples.dart-2.13
+          name: samples.dart