fix(http1): fix preserving header case without enabling ffi (#2820)

The previous commit broke this, but it wasn't released, so released versions will never notice the breakage.

src/client/conn.rs

@@ -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();
                     }