[cmake] Remove deprecated macro add_dumux_test

cmake/modules/DumuxTestMacros.cmake

-###
-# Add a test. All necessary calls to dune CMake macros for adding a
-# test are called from this macro.
-# The added test is automatically build if cmake is invode with the command
-# line argument -DDUMUX_BUILD_ALL_TESTS:BOOL=TRUE otherwise the test is
-# built only when "ctest" / "make test" is invoked.
-# The test is only built if it does not already exist.
-#
-# Arguments:
-# - dumux_test:                   name of the new test
-# - dumux_test_executable:        name of the executable required by the test
-# - dumux_test_executable_source: source file (.cc) of the new test
-# - further arguments:            are optional and are used as arguments for calling the test
-###
-macro(add_dumux_test dumux_test dumux_test_executable dumux_test_executable_source)
-
-  message(WARNING "add_dumux_test is deprecated. Use dumux_add_test now that we require dune 2.6")
-
-  # if present, symlink the grids folder
-  set(grids_directory ${CMAKE_CURRENT_SOURCE_DIR}/grids)
-  if(EXISTS ${grids_directory} AND IS_DIRECTORY ${grids_directory})
-    dune_symlink_to_source_files(FILES grids)
-  endif()
-
-  # if present, symlink the input file
-  set(input_file ${CMAKE_CURRENT_SOURCE_DIR}/${dumux_test_executable}.input)
-  if(NOT EXISTS ${input_file})
-    get_filename_component(base_source_name ${dumux_test_executable_source} NAME_WE)
-    set(input_file ${CMAKE_CURRENT_SOURCE_DIR}/${base_source_name}.input)
-  endif()
-  if(EXISTS ${input_file})
-    # dune symlink takes a path relative to the source directory
-    get_filename_component(input_file ${input_file} NAME_WE)
-    dune_symlink_to_source_files(FILES ${input_file}.input)
-  endif()
-
-  # get optional arguments
-  # cannot use ARGN directly with list() command, copy to a variable first
-  set(dumux_test_args ${ARGN})
-  list(LENGTH dumux_test_args num_dumux_test_args)
-
-  # add executable
-  # check whether executable already exists
-  if(NOT TARGET ${dumux_test_executable})
-    add_executable(${dumux_test_executable} ${dumux_test_executable_source})
-  endif()
-
-  # add test
-  list(GET dumux_test_args 0 dumux_test_command)
-  list(REMOVE_AT dumux_test_args 0)
-  dumux_add_test(NAME ${dumux_test}
-                TARGET ${dumux_test_executable}
-                COMMAND ${dumux_test_command}
-                CMD_ARGS ${dumux_test_args})
-  # tests always require the executable to run
-  set_tests_properties(${dumux_test} PROPERTIES REQUIRED_FILES ${dumux_test_executable})
-endmacro()
-
 # Dumux wrapper for the module that provides tools for testing the Dune way.
 # We have a wrapper to have to possibily of supporting multiple Dune versions.
 #