Add Rémi Delmas as contracts code owner

[tautschnig]

Rémi Delmas is a member of the team working on code contracts, and has
already made a series of contributions to this part of the code base.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• n/a Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Merging #6805 (aed93c8) into develop (351cecb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #6805   +/-   ##
========================================
  Coverage    76.99%   76.99%           
========================================
  Files         1594     1594           
  Lines       184263   184263           
========================================
  Hits        141872   141872           
  Misses       42391    42391           

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