Makefile: Stop installing binaries into source dir
With commit eb6fd605 (Makefile: Stop installing binaries into source dir, 2021-05-07), we stopped installing Gitaly binaries into its root directory given that all users should either use the installed location, or alternatively use the directory in "_build/bin". This change had been reverted due to a regression, where the init.d script in Rails was still using the old location of Gitaly 1. The issue has since been fixed by adjusting paths in the script to point into our build directory.
Reintroduce the change and stop installing binaries into the root directory.