ipfs-1-to-2: remove golang-lru submodule

The submodule is empty and is responsible for the following error:

```
  > go get -u github.com/ipfs/fs-repo-migrations
  # cd /home/christian/gocode/src/github.com/ipfs/fs-repo-migrations; git submodule update --init --recursive
  fatal: no submodule mapping found in .gitmodules for path 'ipfs-1-to-2/golang-lru'
  package github.com/ipfs/fs-repo-migrations: exit status 128
```

Author: chriscool