Remove IWAs from Chrome Tabs category in getDisplayMedia()

Currently, Isolated Web Apps (IWAs) are listed in  Chrome Tab and Window  categories in the getDisplayMedia() media picker. This CL removes IWAs from Chrome Tab category to make them feel more like native apps and to make them act the same way as PWAs when it comes to surface capture.

Bug: b/333377290
Change-Id: Ibad1f0b37cd524ac65be162f956cd82d4349720f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5750144
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Simon Hangl <simonha@google.com>
Commit-Queue: Magdalena Skarbińska <mskarbinska@google.com>
Cr-Commit-Position: refs/heads/main@{#1337254}