message: fix(http1): fix preserving header case without enabling ffi
  The previous commit broke this, but it wasn't released, so released versions will never notice the breakage.
diff: @@ -967,7 +967,6 @@ impl Builder {
  if opts.h1_title_case_headers {
  conn.set_title_case_headers();
  }
  - #[cfg(feature = "ffi")]
  if opts.h1_preserve_header_case {
  conn.set_preserve_header_case();
  }
  