Revert "[2/3][Clang][RISCV] Add __riscv_ for non-overloaded intrinsics"

This reverts commit 2153544.
Buildbot failure https://lab.llvm.org/buildbot#builders/139/builds/35218
shows left-out test cases that were not updated.

Author: eopXD

clang/lib/Support/RISCVVIntrinsicUtils.cpp

@@ -1002,10 +1002,6 @@ void RVVIntrinsic::updateNamesAndPolicy(bool IsMasked, bool HasPolicy,
     OverloadedName += suffix;
   };
 
-  // This follows the naming guideline under riscv-c-api-doc to add the
-  // `__riscv_` suffix for all RVV intrinsics.
-  Name = "__riscv_" + Name;
-
   if (IsMasked) {
     if (PolicyAttrs.isTUMUPolicy())
       appendPolicySuffix("_tumu");