Cleanup `AutoMLSearch` parameters for both `IterativeAlgorithm` and `DefaultAlgorithm`

[chukarsten]

Delete search_iterative().

[chukarsten]

@jeremyliweishih we add this to your epic for when you get around to it!

[jeremyliweishih]

@chukarsten sounds great!

[jeremyliweishih]

@freddyaboulton brought up that we can define a AutoMLAlgorithParameters class and have users specify them there for either the Default/Iterative algorithm. Will consider implementing that in this issue to make AutoMLSearch API less confusing (as there would be parameters specific for each algorithm [allowed_component_graphs being one of them]). If not I will file another issue for tech debt.