Remove myself from Unicode experts

I'm getting too many notifications. I prefer to poll for Unicode
issues, rather than being notified of all Unicode issues.

Author: vstinner

experts.rst

@@ -353,7 +353,7 @@ testing             michael.foord, ezio.melotti
 test coverage
 threads
 time and dates      lemburg, belopolsky, p-ganssle
-unicode             lemburg, ezio.melotti, vstinner, benjamin.peterson,
+unicode             lemburg, ezio.melotti, benjamin.peterson,
 version control     eric.araujo, ezio.melotti
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