Avoid a warning for names in snapshots

[snoyberg]

Since we no longer require this field, the previous code would spit out
a warning if it was present. This is extremely noisy for a field that
used to be required. Instead: just ignore the field if present.

Note: Documentation fixes for https://docs.haskellstack.org/en/stable/ should target the "stable" branch, not master.

Please include the following checklist in your PR:

• Any changes that could be relevant to users have been recorded in the ChangeLog.md
• The documentation has been updated, if necessary.

Please also shortly describe how you tested your change. Bonus points for added tests!