Simplify hard fork logic

[arvidn]

This PR is best reviewed one commit at a time, as the flags are fairly independent.

Now that the hard fork has activated, some feature flags are no longer necessary (as they are always enabled).

ENABLE_SOFTFORK_CONDITION, AGG_SIG_ARGS and COND_ARGS_NIL - these features are always-on now.

The change around AGG_SIG_ARGS and COND_ARGS_NIL is probably the least obvious. Before the hard fork, AGG_SIG_ME and AGG_SIG_UNSAFE required exactly two arguments (as opposed to all other conditions, that allow unknown arguments). When AGG_SIG_ARGS is set (as it is after the hard fork activation), the AGG_SIG_ME and AGG_SIG_UNSAFE conditions behave like the others. This is why the special cases can be removed in conditions.rs, here.

[coveralls-official]

Pull Request Test Coverage Report for Build 9836286700

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 6 of 6 (100.0%) changed or added relevant lines in 2 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+1.9%) to 82.688%

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Files with Coverage Reduction	New Missed Lines	%
crates/chia-consensus/src/gen/conditions.rs	2	99.45%

Totals
Change from base Build 9785517758:	1.9%
Covered Lines:	11554
Relevant Lines:	13973

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💛 - Coveralls