Do not print inferred submodules explicitly in __inferred_module.map

Otherwise including a header in your source file that is not included by
framework's umbrella header will silently add an empty submodule with that
name.

is automatically translated to
@import Foo.NotInModule;

which then would have succeeded because the inferred module map
contained an empty submodule called NotInModule.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207024 91177308-0d34-0410-b5e6-96231b3b80d8