wheezy LTS has ended: remove C# distribtest

tools/dockerfile/distribtest/csharp_wheezy_x64/Dockerfile

@@ -1,20 +0,0 @@
-# Copyright 2015 gRPC authors.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-FROM mono:4.4.2.11
-
-# make sure we have nuget 2.12+ (in case there's an older cached docker image)
-RUN apt-get update && apt-get install -y nuget
-
-RUN apt-get update && apt-get install -y unzip

tools/run_tests/artifacts/distribtest_targets.py

@@ -303,7 +303,6 @@ def targets():
         CppDistribTest('linux', 'x64', 'jessie', 'cmake_as_submodule'),
         CppDistribTest('windows', 'x86', testcase='cmake'),
         CppDistribTest('windows', 'x86', testcase='cmake_as_externalproject'),
-        CSharpDistribTest('linux', 'x64', 'wheezy'),
         CSharpDistribTest('linux', 'x64', 'jessie'),
         CSharpDistribTest('linux', 'x86', 'jessie'),
         CSharpDistribTest('linux', 'x64', 'centos7'),