Remove std/random

[mratsim]

We reintroduced std/random in #2255 to unbreak the unstable branch.

It is used here:

nimbus-eth2/beacon_chain/nimbus_beacon_node.nim

Lines 650 to 664 in 718feef

	# randomize() already called; also, never probe on first epoch in guard
	# period, so that existing, running validators can be picked up. Whilst
	# this reduces entropy for overlapping-start cases, and increases their
	# collision likelihood, that can be compensated for by increasing guard
	# epoch periods by 1. As a corollary, 1 guard epoch won't detect when a
	# duplicate pair overlaps exactly, only the running/starting case. Even
	# 2 epochs is dangerous because it'll guarantee colliding probes in the
	# overlapping case.
	# TODO: is a pseudo-random RNG enough here?
	# If so, should we store the state explicitly?
	# So dPE == 2 -> epoch + 1, always; dPE == 3 -> epoch + (1 or 2), etc.
	node.processor.gossipSlashingProtection.probeEpoch =
	slot.epoch + 1 + rand(duplicateValidatorEpochs.int - 2).uint64

We should remove its usage (except in test) and err on the side of safety.

[tersec]

960666d removes this usage and nimbus_beacon_node's import of random.

Remaining users are:

nimbus-eth2/beacon_chain/validator_duties.nim

Lines 537 to 557 in 960666d

	proc getSlotTimingEntropy(): int64 =
	# Ensure SECONDS_PER_SLOT / ATTESTATION_PRODUCTION_DIVISOR >
	# SECONDS_PER_SLOT / ATTESTATION_ENTROPY_DIVISOR, which will
	# enure that the second condition can't go negative.
	static: doAssert ATTESTATION_ENTROPY_DIVISOR > ATTESTATION_PRODUCTION_DIVISOR
	# For each `slot`, a validator must generate a uniform random variable
	# `slot_timing_entropy` between `(-SECONDS_PER_SLOT /
	# ATTESTATION_ENTROPY_DIVISOR, SECONDS_PER_SLOT /
	# ATTESTATION_ENTROPY_DIVISOR)` with millisecond resolution and using local
	# entropy.
	#
	# Per issue discussion "validators served by the same beacon node can have
	# the same attestation production time, i.e., they can share the source of
	# the entropy and the actual slot_timing_entropy value."
	const
	slot_timing_entropy_upper_bound =
	SECONDS_PER_SLOT.int64 * 1000 div ATTESTATION_ENTROPY_DIVISOR
	slot_timing_entropy_lower_bound = 0-slot_timing_entropy_upper_bound
	rand(range[(slot_timing_entropy_lower_bound + 1) ..
	(slot_timing_entropy_upper_bound - 1)])

nimbus-eth2/beacon_chain/deposit_contract.nim

Lines 259 to 261 in 960666d

	if cfg.maxDelay > 0.0:
	delayGenerator = proc (): chronos.Duration =
	chronos.milliseconds (rand(cfg.minDelay..cfg.maxDelay)*1000).int

nimbus-eth2/beacon_chain/nimbus_binary_common.nim

Lines 44 to 45 in 960666d

	proc setupLogging*(logLevel: string, logFile: Option[OutFile]) =
	randomize()

The last one presumably only supporting the existence of the other two.

With those gone, only cases where Nim PRNG weaknesses don't matter, such as state_sim, block_sim, tests, and benchmarks will use it in the nimbus-eth2 repo itself.

[tersec]

#2442 removes these.