Remove ci_max_artifact_size_lsif limit from docs

What does this MR do?

Related issue: #249561 (closed)

After the recent fix of the in-memory processing, the memory usage reduced significantly for a large file, maybe we can try removing the limit without waiting for gitlab-workhorse#270 (moved). We can always specify it back when/if we see the problems but at the moment the limit is causing more confusion rather than providing value.