bindings: Remove [SecureContext] from IDL dictionaries

IDL dictionary types do not have any representation in ECMAScript,
so [SecureContext] has no effect and meaningless. Remove it.

Change-Id: I1d256c2f6957be3b17a86a725978624374209eb4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4561084


Auto-Submit: Yuki Shiino <yukishiino@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1148380}