Don't use cbmc-developers as a code owner

The GitHub documentation says that in CODEOWNERS you should only
specify people with write access. @diffblue/cbmc-developers does not
have write access. We want to keep the current behaviour that no one is
assigned as code owner, so we leave the list blank instead.

Author: Owen

CODEOWNERS

@@ -47,13 +47,14 @@ src/cpp/ @kroening @tautschnig @peterschrammel
 
 
 # These files change frequently and changes are low-risk
+# The list of usernames/team names deliberately left blank so nobody is assigned as code owner
 
-src/util/irep_ids.def @diffblue/cbmc-developers
+src/util/irep_ids.def
 
-unit/ @diffblue/cbmc-developers
-regression/ @diffblue/cbmc-developers
-jbmc/unit/ @diffblue/cbmc-developers
-jbmc/regression/ @diffblue/cbmc-developers
+unit/
+regression/
+jbmc/unit/
+jbmc/regression/
 
 scripts/ @diffblue/devops @thk123 @forejtv @peterschrammel
 .travis.yml @diffblue/devops @thk123 @forejtv @peterschrammel