Remove transitive mapping tests?

[takikawa]

In the source map hackfest, we discussed that at least browser consumers are unlikely to want to implement transitive mapping (mapping in which source maps map to original sources that themselves have mappings).

We currently do have tests for this case, but maybe we should remove them?

[nicolo-ribaudo]

I think it's valuable to test tools that perform source map composition, and even though the current transitive mappings test is not optimal it maybe helps with that?

[dcrousso]

btw im pretty sure WebKit doesn't support this

it would likely require Web Inspector to actually parse the sourceContent in order to pull out the source map directive/URL instead of just displaying it

unless this is something super commonly used, id be in favor of removing it and not supporting it as that's a nontrivial amount of work to implement