deprecate disallowed-offsets config for re-orgs (#9449)

https://github.com/ethereum/consensus-specs/pull/5348. As per discussions in issue we no longer need to support `disallowed-offsets` for pre-Fulu forks.


  


Co-Authored-By: hopinheimer <knmanas6@gmail.com>

book/src/advanced_re-orgs.md

@@ -11,15 +11,11 @@ attestations and transactions that can be included.
 
 ## Command line flags
 
-There are three flags which control the re-orging behaviour:
+There is one flag which controls the re-orging behaviour:
 
 * `--disable-proposer-reorgs`: turn re-orging off (it's on by default).
-* `--proposer-reorg-disallowed-offsets N1,N2,N3...`: Prohibit Lighthouse from attempting to reorg at
-  specific offsets in each epoch. A disallowed offset `N` prevents reorging blocks from being
-  proposed at any `slot` such that `slot % SLOTS_PER_EPOCH == N`. The value to this flag is a
-  comma-separated list of integer offsets.
 
-All flags should be applied to `lighthouse bn`. The default configuration is recommended as it
+This flag should be applied to `lighthouse bn`. The default configuration is recommended as it
 balances the chance of the re-org succeeding against the chance of failure due to attestations
 arriving late and making the re-org block non-viable.
 
@@ -32,8 +28,6 @@ The full conditions are described in [the spec][] but the most important ones ar
 
 * Only single-slot re-orgs: Lighthouse will build a block at N + 1 to re-org N by building on the
   parent N - 1. The result is a chain with exactly one skipped slot.
-* No epoch boundaries: to ensure that the selected proposer does not change, Lighthouse will
-  not propose a re-orging block in the 0th slot of an epoch.
 
 ## Logs