Remove integrity SHAs for git depedencies

It appears that different machines can produce different hashes for
git-based dependencies, so the npm team moved to completely remove
integrity checksums for them. Apparently these checksums were based
on gzipped archives, which are not guaranteed to be binary identical
for the same inputs across different CPU architectures. There is
still some cryptographic integrity defense as the dependency is
pinned to a git commit and that relies on the entire previous history
of the repo, as discussed in the later parts of this issue on npm.

npm/cli#2846