Fix "alumni team explicitly includes member who was specified as an alumni already in 'libs-api'"

     [WARN  rust_team::validate] couldn't perform checks relying on the Zulip API, some errors will not be detected
     [WARN  rust_team::validate] cause: missing ZULIP_USER and/or ZULIP_TOKEN environment variables
     [ERROR rust_team::validate] validation error: alumni team explicitly includes member 'Kimundi' who was specified as an alumni already in 'libs-api'
     [ERROR rust_team::validate] validation error: alumni team explicitly includes member 'aturon' who was specified as an alumni already in 'libs-api'
     [ERROR rust_team::validate] validation error: alumni team explicitly includes member 'brson' who was specified as an alumni already in 'libs-api'
     [ERROR rust_team] 3 validation errors found

Author: dtolnay

teams/alumni.toml

@@ -7,17 +7,14 @@ name = "alumni"
 leads = []
 members = [
     "Aatch",
-    "Kimundi",
     "MajorBreakfast",
     "QuietMisdreavus",
     "TimNN",
     "alercah",
     "arielb1",
-    "aturon",
     "birkenfeld",
     "bkoropoff",
     "booyaa",
-    "brson",
     "edunham",
     "erickt",
     "frewsxcv",