gitaly-git2go: Cleanup backwards compatibility code
After releasing a new convention on deploying gitaly-git2go during gitaly setup we can now remove ad-hoc fix for detecting proper gitaly-git2go binary and move forward with the new approach only. And as we don't need to have binary path resolution to be exportable we make it package private.
Closes: #3666 (closed)
Changelog: other
Edited by Toon Claes