WebGPU: Add missing destructor for object wrappers. Bug: angleproject:414831373 Change-Id: I65aa17b5cbac2564140491744461bc94e9ae9f2d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6551496 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Liza Burakova <liza@chromium.org>