VCL: X-Cache simplification
- Remove the stacked foo+bar states. Only the final one matters
for most analysis or stats, the rest was about debugging and
understanding varnish behaviors, and we have better ways to do
that without involving runtime headers. This includes removing
the text-specific "+chfp". Each layer now only records one of
four possible states: hit, miss, pass, or int.
- Remove the hit-counter from non-hit states (it's always zero).
- Re-format hit-counter as "hit/N" rather than "hit (N)"
- Remove logic/output for "frontend" (the right-most is always
"frontend", so it's redundant).
With this change, interpretation and accounting for statistical
purposes is greatly simplified.