iobuf: drop dependency to minibytes

Summary:
See previous change for context. This drops the motivation to move `minibytes`
to `folly`, surfaced from sapling discord channel:

> quark — 1:16 PM
> What's the motivation behind moving minibytes? I actually prefer it being part of sapling/ for clearer ownership.
>
> benrogers — 2:02 PM
> https://github.com/search?q=repo%3Afacebook%2Ffolly%20minibytes&type=code
> (iobuf is already in folly and depends on minibytes, so moving minibytes there avoids a circular dependency)

Switching the dependency (minibytes optionally depend on iobuf) is not easy,
because iobuf does not yet have a Cargo.toml, or if it does, it is cross-repo, and
if minibytes uses a git url to refer to iobuf, the git url will prevent us from
publishing minibytes to creates.io.

Reviewed By: muirdm

Differential Revision: D79678310

fbshipit-source-id: f87765a280d6fcef4528eb3555cb1027b8193628

Author: quark-zju

folly/rust/iobuf/BUCK

@@ -88,9 +88,6 @@ fb_xplat_rust_library(
     crate = "iobuf",
     crate_root = "src/lib.rs",
     cxx_bridge = "src/lib.rs",
-    features = [
-        "minibytes",
-    ],
     platforms = (CXX, ANDROID, APPLE, WINDOWS),
     test_deps = [
         "fbsource//third-party/rust:quickcheck",
@@ -102,7 +99,6 @@ fb_xplat_rust_library(
     ],
     xplat_preexisting_target_flavors = [FBCODE],
     deps = [
-        "fbcode//eden/scm/lib/minibytes:minibytes",
         "fbsource//third-party/rust:bytes",
         "fbsource//third-party/rust:cxx",
         "fbsource//third-party/rust:memmap2",

folly/rust/iobuf/src/iobuf.rs

@@ -163,8 +163,6 @@ pub unsafe trait BytesToIOBufSharedExt: std::ops::Deref<Target = [u8]> {}
 
 unsafe impl BytesToIOBufSharedExt for bytes::Bytes {}
 unsafe impl BytesToIOBufSharedExt for memmap2::Mmap {}
-#[cfg(feature = "minibytes")]
-unsafe impl BytesToIOBufSharedExt for minibytes::Bytes {}
 
 /// Convert a `Bytes` into an `IOBufShared`.
 impl<T> From<T> for IOBufShared