spec: do not use 'patch -b' for manual page fixes
    
    The 'make install' target in Makefile is written by hand (not generated by
    automake) and it can't tell whether the backups are/(are not) regular
    manpages.  Thus it would install also all backups as it was manual page.
    
    Detected by RPMDiff (private link):
        https://rpmdiff.lab.eng.brq.redhat.com/run/43086/3/
    
    Version: 9.2.4-4