[llvm] [NFC] Eliminate top-level "using namespace" from some headers. (PR #102751)

[Rahul Joshi via llvm-commits]

================
@@ -46,12 +46,8 @@
 #include <type_traits>
 #include <utility>
 
-namespace llvm {
----------------
jurahul wrote:

These declarations seems unnecessary as they are already provided by the included headers.

https://github.com/llvm/llvm-project/pull/102751