[NFC] Remove unused member variable PolicyBitMask in SemaRecord

Coverity static analysis tool found PolicyBitMask being used
uninitialized in push_back call in RVVEmitter::createRVVIntrinsics()
but this variable has no uses.

Differential revision: https://reviews.llvm.org/D146847

clang/utils/TableGen/RISCVVEmitter.cpp

@@ -57,9 +57,6 @@ struct SemaRecord {
   // Suffix of overloaded intrinsic name.
   SmallVector<PrototypeDescriptor> OverloadedSuffix;
 
-  // BitMask for supported policies.
-  uint16_t PolicyBitMask;
-
   // Number of field, large than 1 if it's segment load/store.
   unsigned NF;