Drop vendorized build mode for adblock extension
    
    Now that all the crates needed for the extension are in Fedora,
    we do not need the ability to build with vendored crates anymore.
    
    Additionally, given that we build this in EPEL for CentOS/RHEL, there
    is no reason for us to support a vendor build there, since we will
    have access to the crate packages in EPEL too.