Remove "ERF allocates incorrect resources" Known Issue

[jack-morrison]

Previously believed to have been a known issue on Summit, this is actually just a tricky jsrun-ism.

A new tutorial has been written about the set of options controlling hardware mapping by way of ERFs:
https://github.com/olcf-tutorials/ERF-CPU-Indexing

Note: Upstream IBM documentation on the cpu_index_using option is incorrect at the time of this writing. A case has been opened with IBM requesting its fix.

In addition to removing this from the "Known Issues" section of the Summit User Guide, the new tutorial should be mentioned where appropriate in the "Running Jobs" section.