git reset <tree-ish> <paths> of addition of a submodule?

git submodule add https://my-git-repo blort
git commit -m 'add a submodule'
git reset HEAD^ blort

The reset deletes the gitlink, but does not delete the entry in
.gitmodules.  On one hand, this is exactly what the user asked for --
they wanted the path 'blort' to be changed in the index, and that's
what they got.  On the other hand, the behavior differs from git rm,
and seems confusing: most folks don't want an entry in .gitmodules
which doesn't correspond to a gitlink.  

If reset isn't the right thing for me to do when I want to say "oops"
about adding a submodule, then what is?  I could do:
git reset HEAD^ blort .gitmodules
but what if I added two submodules and only wanted to undo the addition
of one?