Import upstream v0.16.23, stripped

Upstream commit: 9d1c75ab68435e4417337f768291e5f947686203
Enterprise-only files removed or emptied: 63
Enterprise-only snippets removed: 118 in 50 files
Dangling module declarations removed: 5
Edits turning enterprise off: 25
Third-party code: 14 files, 0 not in THIRD-PARTY.md
Verification: clean

One snippet more than v0.16.22, in crates/common/src/auth/authentication.rs
(3, was 2).

crates/pop3/src/op/fetch.rs

@@ -64,14 +64,8 @@ impl<T: SessionStream> Session<T> {
                         )
                         .get_full_range();
 
-                    self.write_bytes(
-                        Response::Message::<u32> {
-                            bytes,
-                            lines: lines.unwrap_or(0),
-                        }
-                        .serialize(),
-                    )
-                    .await
+                    self.write_bytes(Response::Message::<u32> { bytes, lines }.serialize())
+                        .await
                 } else {
                     Err(trc::Pop3Event::Error
                         .into_err()