devices: vvu-proxy: Use anyhow::Error instead of thiserror
devices: vvu-proxy: Use anyhow::Error instead of thiserror

Use anyhow::Error instead of defining Error enum so that we can provide
more precise error messages easily.

BUG=b:232273004
TEST=run VVU on workstation

Change-Id: I6107fb79b3e7b1a20b11b24c8ec62e2fd8564b78
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3640877
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Auto-Submit: Keiichi Watanabe <815e4e8f7c92a23424d7c3f51ead622bcedbc720@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Keiichi Watanabe <815e4e8f7c92a23424d7c3f51ead622bcedbc720@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm