[llvm] [Offload][NFC] Rename 'omp::target` namespace to `offload` (PR #195682)

[Alex Duran via llvm-commits]

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@@ -45,8 +45,7 @@
 typedef uint64_t (*IdInterfaceTy)();
 
 namespace llvm {
-namespace omp {
-namespace target {
+namespace offload {
 namespace ompt {
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adurang wrote:

What this one (and the followin two) are inside the OpenMP specific headers, shouldn't they remain as such? 

https://github.com/llvm/llvm-project/pull/195682