encoding: fix make build by removing local-encoding

Summary:
`local-encoding` was removed in D67531801, let's remove it from autocargo. Otherwise, it will cause the following error when running `make local` on dev server:
```
error: no matching package named `local-encoding` found
location searched: directory source `(redacted)/third-party/rust/vendor` (which is replacing registry `crates-io`)
required by package `sapling-encoding v0.1.0
...
```

Reviewed By: muirdm

Differential Revision: D68019676

fbshipit-source-id: 760be12a3d822bf9b7351491250c50c957b5218b

Author: zzl0

eden/scm/lib/encoding/Cargo.toml

@@ -19,5 +19,4 @@ sapling-types = { version = "0.1.0", path = "../types" }
 winapi = { version = "0.3", features = ["everything", "std"] }
 
 [target.'cfg(windows)'.dependencies]
-local-encoding = "*"
 winapi = "0.3"