Remove announce@apache.org in generate-email.sh

`announce@apache.org` requires the sender to have an `@apache.org`
address. Not all PMC members have this configured, this adds yet
another step to the release process and yet another condition to
hold in the RM machine, and people are not willing to drop this
requirement[1].

[1] https://lists.apache.org/thread/jc7o25gxx9w3y3xq51kwbmcbz62cwkb2

.github/generate-email.sh

@@ -106,7 +106,7 @@ EOF
 
 announce)
     cat <<EOF
-To: announce@apache.org, log4j-user@logging.apache.org, dev@logging.apache.org
+To: log4j-user@logging.apache.org, dev@logging.apache.org
 Title: [ANNOUNCE] $PROJECT_NAME $PROJECT_VERSION released
 
 ${PROJECT_NAME} team is pleased to announce the $PROJECT_VERSION