Revert "[Clang][RISCV] Introduce tuple types for RVV bfloat16 (#72216)" (#72367)

This reverts commit 8434b0b9. #72216 

This commit broke the multiple buildbots, looks like the extension in
`NUM_PREDEF_TYPE_IDS` might have broken some inheriting usages, causing
indeterminate results for the compiler. Investigating the issue now.