Make list::remove/remove_if/unique all return void before C++20; undoes that bit of D58332. Thanks to Mikhail Maltsev for pointing this out

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@365261 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed