remove unneccesary submodules

this still doesn't work. A git submodule sync ; git submodule update --recursive --init in a fresh checkout gives

$ git submodule update --recursive --init 
Submodule 'ledger/ledger-app' (https://github.com/obsidiansystems/ledger-app-tezos.git) registered for path 'ledger/ledger-app'
Submodule 'ledger/nanos-secure-sdk' (https://github.com/LedgerHQ/nanos-secure-sdk.git) registered for path 'ledger/nanos-secure-sdk'
fatal: No url found for submodule path 'opam2nix' in .gitmodules

after git rm ing the offending, now missing submodules, the build fails. There's not actually any ob thunks here yet.

[dbornside@bornside tezos-baking-platform]$ git status
On branch ae-thunkify
Your branch is up-to-date with 'origin/ae-thunkify'.

Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

	deleted:    opam2nix
	deleted:    opam2nix-packages
	deleted:    tezos-bake-monitor
	deleted:    tezos-load-testing

[dbornside@bornside tezos-baking-platform]$ nix-build 
error: getting status of '/home/dbornside/src/testing/tezos-baking-platform/tezos-bake-monitor': No such file or directory