SPEC: Remove unnecessary requirements
    
    We do not need to requires specific version of libldb
    or libtdb because it is automatically detected from
    binary/library dependencies. We also need never version
    of that libraries as it was specified in spec file.
    
    e.g.
      sh$ rpm -q --requires sssd-common | grep -E "TDB|LDB"
      libldb.so.1(LDB_0.9.10)(64bit)
      libtdb.so.1(TDB_1.2.1)(64bit)
    
    There is also redundant dependency on sssd-common-pac
    sssd -> sssd-ipa -> sssd-common-pac
         -> sssd-ad -> sssd-common-pac
         -> sssd-common-pac
    
      sh$ rpm -q --whatrequires sssd-common-pac
      sssd-ipa-1.13.3-1.fc23.x86_64
      sssd-ad-1.13.3-1.fc23.x86_64
      sssd-1.13.3-1.fc23.x86_64
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>