people: Revert to using `ignore_missing` parameter.

We revert to use `ignore_missing` parameter for `maybe_get_user_by_id`
function to avoid sending unnecessary `blueslip.error()` calls to
sentry.

web/src/people.ts

@@ -121,8 +121,8 @@ export function get_by_user_id(user_id: number): User {
 }
 
 // This is type unsafe version of get_by_user_id for the callers that expects undefined values.
-export function maybe_get_user_by_id(user_id: number): User | undefined {
-    if (!people_by_user_id_dict.has(user_id)) {
+export function maybe_get_user_by_id(user_id: number, ignore_missing = false): User | undefined {
+    if (!people_by_user_id_dict.has(user_id) && !ignore_missing) {
         blueslip.error("Unknown user_id in maybe_get_user_by_id", {user_id});
         return undefined;
     }

web/src/presence.js

@@ -175,7 +175,7 @@ export function set_info(presences, server_timestamp) {
         // reload_state.is_in_progress, because races where presence
         // returns data on users not yet received via the server_events
         // system are common in both situations.
-        const person = people.maybe_get_user_by_id(user_id);
+        const person = people.maybe_get_user_by_id(user_id, true);
         if (person === undefined) {
             if (!(watchdog.suspects_user_is_offline() || reload_state.is_in_progress())) {
                 // If we're online, and we get a user who we don't

web/src/rendered_markdown.js

@@ -107,7 +107,7 @@ export const update_elements = ($content) => {
             // mention text to show the user's current name,
             // assuming that you're not searching for text
             // inside the highlight.
-            const person = people.maybe_get_user_by_id(user_id);
+            const person = people.maybe_get_user_by_id(user_id, true);
             if (person !== undefined) {
                 // Note that person might be undefined in some
                 // unpleasant corner cases involving data import.

web/tests/presence.test.js

@@ -95,7 +95,6 @@ test("unknown user", ({override}) => {
     const presences = {};
     presences[unknown_user_id.toString()] = "does-not-matter";
 
-    blueslip.expect("error", "Unknown user_id in maybe_get_user_by_id", 3);
     blueslip.expect("error", "Unknown user ID in presence data");
     presence.set_info(presences, now);