Deprecate and disallow `ctest_empty_binary_directory` command.
The ctest_empty_binary_directory
removes the content of a directory iff the directory contains a CMakeCache.txt
file. It may be used in CTest dashboard scripts to make a clean build.
Since CTest will create the binary directory if it does not exist, it is possible to remove the build directory instead of clearing it.
CTest dashboard scripts can be used for non-CMake projects. Those projects do not generate a CMakeCache.txt
in the binary directory.
It is probably better to recommend using file(REMOVE_RECURSE)
for doing a clean build.