Disable module maps feature since it is not supported by the toolchain

[Hallot]

Fix for https://github.com/grailbio/bazel-compilation-database/issues/101

See https://github.com/bazelbuild/rules_cc/blob/2f8c04c04462ab83c545ab14c0da68c3b4c96191/examples/my_c_compile/my_c_compile.bzl for instance.

I haven't found what this feature actually does or whether it is an issue not to support it.
They do that in the CC example, so I would assume it is for other languages than C/C++?