cut legacy backcompat alias folly::io::CodecType

Summary: All uses have been migrated so the unused alias may now be removed.

Reviewed By: Gownta

Differential Revision: D70042401

fbshipit-source-id: 8350349cecc077dbb84673dc5e1e6c0cc258cf33

folly/compression/Compression.h

@@ -541,5 +541,5 @@ bool hasStreamCodec(CodecType type);
 } // namespace folly
 
 namespace folly::io {
-using folly::compression::CodecType;
+// empty
 } // namespace folly::io