update versioninfo() output. Remove the storage of .githash

[krasow]

requires legate_branch: update-preference-version

[krasow]

Addresses #124 by removing .githash as a file. versioninfo() will now check the git hash dynamically if cuNumeric is in a git repo. However, it will fallback to nothing if it isn't in a git repo. You will need to depend on the specific version output when this occurs.