Remove related item510 note

@eshadatta, @ckassel

Hi Esha,
I'm prepping WIPs for the fales/io collection, and ran into some MODS validation errors when transforming 510 fields. Instead of asking you to look at and fix the stylesheet, I wanted to take a whack at figuring it out myself. The cause of the error, per Oxygen, is that `<note>` elements cannot be nested.

I tweaked the stylesheet in the branch attached to this PR. The change is minor, I just commented out the
`<note>` and `</note>` tags around the `relatedItem510` template.  The MODS generated by the modified stylesheet validates against the schema.

I'm not an XSL-master by any stretch, so would you mind taking a look at this PR?
I used GitHub b/c it's easy to see the modifications I made to the XSL and also the differences
in the MODS.

Please let me know if you have any questions or concerns with my modifications.
If you think the modifications are OK, please let me know that as well and I will merge 
the changes into the R* toolchain.

Thank you for your time!
Joe