drop superfluous call of headers_check
    
    headers_check is run twice when building the kernel rpms.
    
    CONFIG_HEADERS_CHECK is already set to "y" in config-generic. But there
    are also a few lines in kernel.spec where headers_check is invoked again.
    
    Also
    
        grep -q exist hdrwarnings.txt
    
    will never match as errors aren't redirected to hdrwarnings.txt