remove source for CI images

base-10/Dockerfile

base-10/opts.clang

base-10/opts.gcc

base-10/opts.gcc.c++17

base-16.04/Dockerfile

base-16.04/opts.clang

base-16.04/opts.gcc

base-18.04/Dockerfile

base-18.04/opts.clang

base-18.04/opts.gcc

base-18.04/opts.gcc.c++17

base-8-backports/Dockerfile

base-8-backports/opts.clang

base-8/Dockerfile

base-8/opts.clang

base-8/opts.gcc

base-9/Dockerfile

base-9/opts.clang

base-9/opts.gcc

base-common/dune-ctest