delete GuestErrorConversion from docs, tests

crates/wiggle/tests/wasi.rs

@@ -1,4 +1,4 @@
-use wiggle::{GuestError, GuestErrorType, GuestPtr, GuestSlice};
+use wiggle::{GuestErrorType, GuestPtr, GuestSlice};
 use wiggle_test::WasiCtx;
 
 // This test file exists to make sure that the entire `wasi.witx` file can be
@@ -31,13 +31,6 @@ impl GuestErrorType for types::Errno {
     }
 }
 
-impl<'a> types::GuestErrorConversion for WasiCtx<'a> {
-    fn into_errno(&self, e: GuestError) -> types::Errno {
-        eprintln!("GuestError {:?}", e);
-        types::Errno::Badf
-    }
-}
-
 impl<'a> crate::wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx<'a> {
     fn args_get(&self, _argv: &GuestPtr<GuestPtr<u8>>, _argv_buf: &GuestPtr<u8>) -> Result<()> {
         unimplemented!("args_get")