[chromecast] Disable v8_use_external_startup_data

This wasn't working correctly on some architectures. Previous versions
of mediashell had this disabled (b/162594574) because of issues on
64-bit architectures, so this is aligning the chromium browser with
what we had already been doing before.

Bug: 419216998
Test: re-build cast_browser_dist_aar, build mediashell + launch web app
Change-Id: Ibe878def128472e20809ebb9cba10934b7fcfd73
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6580799
Reviewed-by: Sandeep Vijayasekar <sandv@google.com>
Commit-Queue: Simeon Anfinrud <sanfin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1464376}

chromecast/build/args/config/android.gni

@@ -12,3 +12,4 @@ enable_extensions = false
 enable_pdf = false
 enable_plugins = false
 enable_printing = false
+v8_use_external_startup_data = false