Ensure the module slot in R2R image can be located (dotnet/coreclr#7875)

Ensure the module slot in R2R image can be located (dotnet/coreclr#7875)

Each Ready-to-Run image has a slot for storing a pointer to the Module
object associated with this image. However, if the image contains no
code (e.g., facade assemblies), the import table needed to locate
this slot wasn't written out, so the runtime couldn't find this slot.
This casued "crossgen /createpdb" command to fail on facade assemblies
after PR dotnet/coreclr#7809, and required a workaround (commit c4d8994).

This commit ensures writing the import table needed to locate the
slot for module. It also removes the workaround in commit c4d8994,
which is no longer necessary.

Commit migrated from https://github.com/dotnet/coreclr/commit/7d945336a9307eaaf59f985e4ec2c1b5b8c052b4