setup: don't modify repo in `create_reference_database()`

The `create_reference_database()` function is used to create the reference database during initialization of a repository. The function calls `repo_set_ref_storage_format()` to set the repositories reference format. This is an unexpected side-effect of the function. More so because the function is only called in two locations: 1. During git-init(1) where the value is propagated from the `struct repository_format repo_fmt` value. 2. During git-clone(1) where the value is propagated from the `the_repository` value. The former is valid, however the flow already calls `repo_set_ref_storage_format()`, so this effort is simply duplicated. The latter sets the existing value in `the_repository` back to itself. While this is okay for now, introduction of more fields in `repo_set_ref_storage_format()` would cause issues, especially dynamically allocated strings, where we would free/allocate the same string back into `the_repostiory`. To avoid all this confusion, clean up the function to no longer take in and set the repo's reference storage format. Signed-off-by: Karthik Nayak <karthik.188@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>