Remove fullscreen popups experimental feature.

Removes the fullscreen popups feature. This is mainly a revert of
crrev.com/c/4072455 and some followup CLs. Removes feature flag,
tests, UMA metrics and all of the navigation "is_fullscreen" plumbing to support the feature.

See: https://chromestatus.com/feature/6002307972464640

Bug: 345222811
Change-Id: I7994a18a8473407050ae5ec0a732df4d73732776
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5617224
Reviewed-by: Mike Wasserman <[email protected]>
Reviewed-by: Avi Drissman <[email protected]>
Reviewed-by: Robert Kaplow <[email protected]>
Reviewed-by: Nate Chapin <[email protected]>
Commit-Queue: Brad Triebwasser <[email protected]>
Reviewed-by: Elly FJ <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1313712}

window-management/resources/helpers.js

@@ -65,13 +65,10 @@ async function poll(condition, interval = 100, duration = 3000) {
 }
 
 // Open and return a popup on `screen`, optionally asserting placement.
-async function openPopupOnScreen(screen, assertPlacement = true, fullscreen = false) {
+async function openPopupOnScreen(screen, assertPlacement = true) {
   const left = screen.availLeft + Math.floor(screen.availWidth / 2) - 150;
   const top = screen.availTop + Math.floor(screen.availHeight / 2) - 50;
   let features = `left=${left},top=${top},width=300,height=100`;
-  if (fullscreen) {
-    features += ",fullscreen";
-  }
   log(`Opening a popup with features '${features}' on ${screenLog(screen)}`);
   // Window.open() synchronously returns a Window with estimated screenLeft|Top,
   // which may be clamped to the opener's screen or incompletely initialized.