build-configs: riscv: drop LLVM_IAS=1

According to ClangBuiltLinux folks, this is not needed for v5.4+,
and clang builds are not enabled for riscv before that.

Signed-off-by: Kevin Hilman <[email protected]>

Author: khilman

config/core/build-configs.yaml

@@ -387,8 +387,6 @@ build_environments:
       riscv:
         <<: *riscv_params
         name:
-        opts:
-          LLVM_IAS: '1'
 
   clang-16:
     cc: clang