remove redundant bibcode URLs

[GlazerMann]

Existing code does not drop urls if the bibcode parameter is set already.
New code drops url (only after making sure the new and old bibcode match of course).

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@6748cf6). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master    #1419   +/-   ##
=========================================
  Coverage          ?   81.87%           
  Complexity        ?     1861           
=========================================
  Files             ?       10           
  Lines             ?     4017           
  Branches          ?        0           
=========================================
  Hits              ?     3289           
  Misses            ?      728           
  Partials          ?        0

Impacted Files	Coverage Δ	Complexity Δ
Template.php	82.04% <0%> (ø)	1744 <0> (?)

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