fix: update current http urls as per #960

[LexLuthr]

Fixes part of #960

[dirkmc]

I suggest we

• remove the format parameter from the /piece endpoint, as it can only ever have one value so it's redundant
• remove all code related to building car files
• note that we should also remove any methods from HttpServerApi and its implementation that are no longer used

We can always find this code in the commit history if we need it later

[LexLuthr]

@jacobheun Please let me know what's the final call on Dirk's comment. It makes sense to remove that param as it is not adding any value.

[jacobheun]

@LexLuthr agreed on removing it as there's only 1 option.

[dirkmc]

Let's remove PiecesContainingMultihash and GetMaxPieceOffset from HttpServerApi as they are no longer used.
Let's also remove the implementations from serverApi