Bug 28315: Remove duplicate function definition

Bug 28315: Remove duplicate function definition

This patch removes the unnecessary second definition of the JS function PopupMARCFieldDoc from addbiblio.tt.
To test:
1. Apply the patch
2. Check that addbiblio.tt contains only one function definition for PopupMARCFieldDoc
3. Navigate to "Cataloging" -> "Add MARC record"
4. Check that after clicking on the question mark symbol next to any MARC field, the loc description of that MARC field is opened in a new tab

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit a2b880e57bb1ccd4b8270ec8bfdcdc86e18a2e48)
Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>