Remove `FD_RUNTIME_INITIAL_BLOCK_ID`

[mmcgee-jump]

/* The initial block id hash is a dummy value for the initial block id
   as one is not provided in snapshots.  This does not have an
   equivalent in Agave.

   TODO: This should be removed in favor of repairing the last shred of
   the snapshot slot to get the actual block id of the snapshot slot. */

#define FD_RUNTIME_INITIAL_BLOCK_ID (0xF17EDA2CE7B1DUL)