Revert "[libc] Migrate to using LIBC_NAMESPACE_DECL for namespace declaration" (#98593)

Reverts llvm/llvm-project#98075

bots are broken

libc/fuzzing/__support/hashtable_fuzz.cpp

@@ -12,9 +12,8 @@
 #include "include/llvm-libc-types/ENTRY.h"
 #include "src/__support/CPP/string_view.h"
 #include "src/__support/HashTable/table.h"
-#include "src/__support/macros/config.h"
 
-namespace LIBC_NAMESPACE_DECL {
+namespace LIBC_NAMESPACE {
 
 // A fuzzing payload starts with
 // - uint16_t: initial capacity for table A
@@ -180,4 +179,4 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
   return 0;
 }
 
-} // namespace LIBC_NAMESPACE_DECL
+} // namespace LIBC_NAMESPACE