Bugfix/1946 double warnings

[bob-carpenter]

Submisison Checklist

• Run unit tests: ./runTests.py src/test/unit
• Run cpplint: make cpplint
• Declare copyright holder and open-source license: see below

Summary

Remove duplicate warnings in expressions.

Intended Effect

See summary.

How to Verify

Unit test from @ariddell's issue.

Side Effects

No.

Documentation

n/a

Reviewer Suggestions

Anyone.

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company):

Columbia University

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[bob-carpenter]

Not sure what's up. I think I branched this from the other pending pull request's branch, feature/1940-prob-syntax-warn --- not sure why it wants to merge it into develop

[bob-carpenter]

This looks like another Travis failure. @syclik --- could you confirm?

[bob-carpenter]

@syclik Could you re-kick-off the Travis job? I don't seem to have permissions. Or wait until others have finished. Somehow my latest pull request got through Travis first, so they must not be going in order of being called or must have wildly different execution speeds.