[inert] Replace mentions of "expressly inert" with "inert"

The concept of "expressly inert" in the HTML spec was a remnant from the
past. It no longer made sense, and wasn't implemented anywhere.

I removed it in whatwg/html#7565

This patch replaces all mentions with just "inert".

No change in behavior.

Bug: 692360
Change-Id: I5bb76e633b13ee244eb69ad5e99ce9d9705073aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3438605
Reviewed-by: Aaron Leventhal <[email protected]>
Commit-Queue: Oriol Brufau <[email protected]>
Cr-Commit-Position: refs/heads/main@{#968045}

html/interaction/focus/processing-model/focus-fixup-rule-one-no-dialogs.html

@@ -31,7 +31,7 @@
   assert_not_equals(document.activeElement, button, "After disabling, the button must no longer be focused");
   assert_equals(document.activeElement, document.body, "After disabling, the body must be focused");
 
-}, "Disabling the active element (making it expressly inert)");
+}, "Disabling the active element (making it inert)");
 
 test(() => {
   const button = document.querySelector("#button2");

inert/dynamic-inert-on-focused-element.tentative.html

@@ -3,7 +3,7 @@
 <title>Dynamic inertness on focused element</title>
 <link rel="author" title="Oriol Brufau" href="mailto:[email protected]">
 <link rel="help" href="https://html.spec.whatwg.org/multipage/interaction.html#focus-fixup-rule">
-<meta name="assert" content="If a focused element becomes expressly inert, it stops being focused.">
+<meta name="assert" content="If a focused element becomes inert, it stops being focused.">
 <div id="log"></div>
 
 <div class="test-wrapper" data-name="<input> that gets 'inert' attribute">