Remove Ben Barham from code owners

Author: bnbarham

.github/CODEOWNERS

@@ -8,7 +8,7 @@
 # Order is important. The last matching pattern has the most precedence.
 
 # Owner of anything in SwiftSyntax not owned by anyone else.
-* @ahoppen @bnbarham @hamishknight @rintaro
+* @ahoppen @hamishknight @rintaro
 
 # Macros
 /Sources/SwiftSyntaxMacros @DougGregor