After SERVER-76935 kExternalAborted index build state indicates that the caller is responsible for the abort. Still, there are some left over places where we could remove use of IndexBuildAborted.

https://github.com/10gen/mongo/blob/b32042b0dc2f06a56356eb6a6864394b4af46069/src/mongo/db/index_builds_coordinator_mongod.cpp#L761

https://github.com/10gen/mongo/blob/b32042b0dc2f06a56356eb6a6864394b4af46069/src/mongo/db/index_builds_coordinator.cpp#L3347

Maybe we could even just pass the default Interrupted error code in killOp

https://github.com/10gen/mongo/blob/b32042b0dc2f06a56356eb6a6864394b4af46069/src/mongo/db/repl_index_build_state.cpp#L551

Original description:

We use IndexBuildAborted to signal to the index builder thread that "the caller is taking responsibility for aborting this index build, do not cleanup". Instead, we should use the ReplIndexBuildState we already pass around and store this information on that structure, rather than using a special error code.