tidy: Replace custom panic/unwrap lint with clippy lint (#38593)

This change replaces our custom `panic` / `unwrap` lint with the one
from clippy. This rule as not properly applied in servoshell, so this
change fixes some clippy errors raised by the new configuration.

Testing: This change removes the tidy tests for the custom lints, but
otherwise the behavior is tested as part of clippy itself.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/constellation/Cargo.toml

@@ -20,6 +20,10 @@ vello = ["canvas/vello"]
 vello_cpu = ["canvas/vello_cpu"]
 raqote = ["canvas/raqote"]
 
+[lints.clippy]
+unwrap_used = "deny"
+panic = "deny"
+
 [dependencies]
 background_hang_monitor = { path = "../background_hang_monitor" }
 background_hang_monitor_api = { workspace = true }