[doc] Remove unnecessary FIXME

[nyunyunyunyu]

These places don't really need changes. The comments just note that we should be careful.

closes INT-3019
closes INT-3021

[github-actions]

group	app.proof_time_ms	app.cycles	app.cells_used	leaf.proof_time_ms	leaf.cycles	leaf.cells_used
verify_fibair	(+5 [+0.1%]) 3,414	711,180	25,509,905	-	-	-
fibonacci_program	6,113	1,500,137	51,505,102	-	-	-
regex_program	(+37 [+0.2%]) 18,864	4,190,904	165,028,173	-	-	-
ecrecover_program	(-5 [-0.2%]) 2,630	285,401	15,092,297	-	-	-

Commit: fd19628

Benchmark Workflow