message_edit: Refactor do_update_mobile_push_notification for clarity.
message_edit: Refactor do_update_mobile_push_notification for clarity.

This is a prep commit of #18917.

andersk/zulip,eeshangarg/zulip,zulip/zulip,hackerkid/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,kou/zulip,kou/zulip,hackerkid/zulip,punchagan/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,zulip/zulip,kou/zulip,hackerkid/zulip,eeshangarg/zulip,hackerkid/zulip,punchagan/zulip,zulip/zulip,andersk/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,punchagan/zulip,hackerkid/zulip,punchagan/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,hackerkid/zulip,punchagan/zulip,andersk/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,rht/zulip,rht/zulip,andersk/zulip,kou/zulip,kou/zulip,rht/zulip,eeshangarg/zulip