On https://chromium-review.googlesource.com/c/chromium/src/+/1347283, my chromium.org account is a reviewer, and my Google.com account is CCed (The latter probably happened because I was forced to log in with my Google account, due to lack of an account selection option, despite being logged into both accounts according to bugs.chromium.org).

Regardless of how it happened, I'm unable to remove my google.com address from the CC list.  When logged into my chromium.org account, I get an unable to remove reviewers error when I try to send a message and remove my google.com address from the CC (not reviewer) list.  From my google.com, I get the same error.  The latter seems like it's pretty definitively a bug - people should always be able to remove themselves from CC lists.