[css-syntax] "5.1 Parser Railroad Diagrams"

In section "5.1 Parser Railroad Diagrams", railroads diagrams are 
compared to (presumably finite) state-machines and regular expressions. 
This is misleading: neither regular expressions nor finite 
state-machines have the same expressive power as the railroad diagrams 
used in section 5.1 (regular versus context-free languages).

Drop the comparision in section 5.1.

Note, though, that the analogous description in section "4.1 Token 
Railroad Diagrams" is correct in that particular situation (although not 
valid in general).