fix(ipx): allow overriding baseURL regardless of router base

[jeanmatthieud]

#483

Removing this non existing context variable use allows the proper configuration of the baseURL variable, and, at the same time, the use of an external IPX server.

[pi0]

Thanks. I've fixed types and made modification to still be able completely override baseURL still respect router base when generating default _ipx endpoint.

[chrisspiegl]

I just tried this out and first thought I could not use baseURL with the IPX and thus use an external IPX server because the baseURL seems to not be included in the typescript type of IPXOptions?