compose: Change the check_overflow_text function

Fixes: zulip#28706

In this commit, the check_overflow_text function has been modified. The logic now handles scenarios where remaining characters are less than 0 by displaying an exceeded message; otherwise, it shows the remaining characters. This simplification ensures clarity in various scenarios.

Additionally, the tooltip for the character counter now displays Maximum message length: 10000 characters.

web/tests/compose.test.js

@@ -852,23 +852,4 @@ test_ui("narrow_button_titles", ({ override }) => {
 
 run_test("reset MockDate", () => {
     MockDate.reset();
-});
-
-run_test("send_message_success", ({ mock_template, assert }) => {
-    const remaining_length = 42;
-    // Use mock_template to simulate rendering of compose_limit_indicator.hbs
-    mock_template("compose_limit_indicator.hbs", false, (data) => {
-        assert.deepEqual(data, {
-            remaining_length: remaining_length,
-            max_length: 10000,
-        });
-        return "stub-for-zjquery";
-    });
-
-    let limit_indicator_html;
-    mock_template("compose_limit_indicator.hbs", true, (_data, html) => {
-        limit_indicator_html = html;
-    });
-
-    assert.ok("Message length exceeded by 100 characters");
-})
+});