cleanup dockerfiles and scripts for old interop infrastructure

tools/README.md

tools/dockerfile/grpc_csharp_mono/Dockerfile

tools/dockerfile/grpc_csharp_mono/build.sh

tools/dockerfile/grpc_csharp_mono_base/Dockerfile

tools/dockerfile/grpc_cxx/Dockerfile

tools/dockerfile/grpc_cxx/build.sh

tools/dockerfile/grpc_go/Dockerfile

tools/dockerfile/grpc_go/README.md

tools/dockerfile/grpc_go/build.sh

tools/dockerfile/grpc_java/Dockerfile

tools/dockerfile/grpc_java/README.md

tools/dockerfile/grpc_java/build.sh

tools/dockerfile/grpc_node/Dockerfile

tools/dockerfile/grpc_node/build.sh

tools/dockerfile/grpc_node_base/Dockerfile

tools/dockerfile/grpc_php/Dockerfile

tools/dockerfile/grpc_php/README.md

tools/dockerfile/grpc_php/build.sh

tools/dockerfile/grpc_php_base/Dockerfile

tools/dockerfile/grpc_php_base/README.md