[libcxx] Remove dynarray

Summary:
std::dynarray had been proposed for C++14, but it was pulled out from C++14
and there are no plans to standardize it anymore.

Reviewers: mclow.lists, EricWF

Subscribers: mgorny, christof, jkorous, dexonsmith, arphaman, libcxx-commits

Differential Revision: https://reviews.llvm.org/D54801

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@347783 91177308-0d34-0410-b5e6-96231b3b80d8

include/module.modulemap

@@ -524,10 +524,6 @@ module std [system] {
       header "experimental/deque"
       export *
     }
-    module dynarray {
-      header "experimental/dynarray"
-      export *
-    }
     module filesystem {
       header "experimental/filesystem"
       export *