Drop credential-gnome-keyring, but keep support for older OSs
    
    Since the libsecret replaces the libgnome-keyring,
    the libgnome-keyring is not necessary to keep it in the git package.
    In addition, gnome-keyring is deprecated and according to people
    from GNOME, they do not expect that anyone would want to use the old
    library when libsecret is installed. So drop credentials for
    libgnome-keyring.
    
    However, I keep that credential in spec for older systems where it
    has been originally, but it is split into the separate rpm, so at
    least it will not be required by the git package. It can be removed
    later.