Remove TODO file.

All remaining tasks are now part of #28632.

PADDING_TODO.txt

-TODO sketch for this branch, in rough priority order:
-
-- Clean up/fix XXX's and FIXMEs
-  - Test event entry points into circuitpad?
-    - Most of our events come from completely untested code :/
-
-- Compat-breaking changes to be decided/done ASAP
-  - Option to keep circuits open if machine present
-  - Specify an ordered preference list of padding machines
-  - Specify exit policy for machine conditions?
-    - short_policy_t looks good, except for its flexible array member :/
-      - Can we make our own struct with a small, fixed number of policy
-        entries? Say 3-4? Or is that a bad idea to lose this flexibility?
-    - Check conditions based on attached streams on the circuit
-      - Accept should mean "only apply if matched"
-      - Reject should mean "don't apply if matched"
-      - If a policy is specified, Reject *:* is implicit default (so reject
-        policies need an Accept entry).
-      - With no policy, Accept *:* is implicit default.
-
-
-- Misc fixes:
-  - Remove circuitsetup machine (but place it in unittests -- they depend on it)
-  - Circuit RTT measurement will break on var_cell/EXTEND2 cells
-    - Are there any heuristics we can use here?
-      - If RELAY_EARLY is only for the first cell of an EXTEND2 series,
-        we can use that. But the proposal currently says MAY, but not MUST
-        for this behavior.
-
-======== 0.3.6 ========
-
-- Come up with some good histograms for eg circuit setup fingerprinting,
-  website fingerprinting, and vanguards usage.
-
-- Vanguards compatibility for MiddleNodes (via changes to vanguards addon)
-
-- circpad_machine_validate() function to sanity-check histograms loaded from
-  consensus/torrc (can also be used to help guide a GA).
-  - Check bin construction
-  - no type overflow (start_usec + range_sec, etc)
-  - no conflicting state transitions (or overlap with cancel events)
-  - no use of both histograms and iat_dist
-  - at least two histogram bins
-  - min_hop vs target_hop
-
-- Support torrc load+serialization of state machines
-  - ??
-
-- Support consensus load+serialization of state machines
-  - ??
-
-- Prop #265 load balancing
-
-- Rephist timer stats
-  - Is this a privacy risk? The adversary could create lots of circuits
-    to find a layer2 vanguard.. Otherwise they will be spread across middles.
-
-