chore: delete poseidon2 from bn254_blackbox_solver

[TomAFrench]

This is no longer needed post #8740 and so is dead code

[github-actions]

Changes to circuit sizes

Generated at commit: 3052b9560de07d747fcb333295ce265ee65d3e24, compared to commit: 150776269b557703552826f90915c85adb639137

🧾 Summary (100% most significant diffs)

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
rollup_base	+835 ❌	+0.20%	+1,500 ❌	+0.04%
rollup_merge	+47 ❌	+3.27%	+85 ❌	+0.00%
parity_root	+71 ❌	+3.48%	+130 ❌	+0.00%
rollup_block_root	+47 ❌	+2.45%	+85 ❌	+0.00%
rollup_root	+23 ❌	+0.12%	+44 ❌	+0.00%
rollup_block_merge	+23 ❌	+0.12%	+44 ❌	+0.00%
parity_base	+71 ❌	+3.52%	0 ➖	0.00%

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Full diff report 👇

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
rollup_base	423,026 (+835)	+0.20%	3,734,618 (+1,500)	+0.04%
rollup_merge	1,483 (+47)	+3.27%	2,751,380 (+85)	+0.00%
parity_root	2,114 (+71)	+3.48%	5,486,624 (+130)	+0.00%
rollup_block_root	1,966 (+47)	+2.45%	4,121,078 (+85)	+0.00%
rollup_root	18,774 (+23)	+0.12%	2,787,535 (+44)	+0.00%
rollup_block_merge	18,790 (+23)	+0.12%	2,787,567 (+44)	+0.00%
parity_base	2,089 (+71)	+3.52%	53,444 (0)	0.00%