exo: Don't double-free wayland proxies in the fuzzer::Harness

Libwayland frees its proxies when the wl_display disconnects. As such
the harness was double-freeing those proxies itself.

Bug: b:283629115
Change-Id: Id87383e20e133d6577adf09c5280b2e17a4598e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4549020


Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1147898}