Remove some trivial transmutes

[apasel422]

No description provided.

[rust-highfive]

r? @brson

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[apasel422]

Outside of test code, there are two remaining uses of std::mem::transmute_copy in the entire repo: the default implementation of Repr::repr in libcore/raw.rs and the str::split_at_mut method in libcore/str/mod.rs. For the latter, the corresponding method for [T] is implemented using raw pointers instead.

[bluss]

@bors r+

Great! Sounds like we should fix str::split_at_mut too

[bors]

📌 Commit 6031a58 has been approved by bluss

[bors]

⌛ Testing commit 6031a58 with merge 140e793...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt