Cleanup hashBvGlobalData

Cleanup hashBvGlobalData

Each compiler object contains a hashBvGlobalData that's 80 bytes in size. Only 16 bytes are actually used - the hash and node free lists.
* hbvFreeVectorList is supposed to be used by hashBv::freeVector but nothing calls that and getNewVector does not attempt to use the free list
* hbvHashSizeLog2 is always 0
* hashBvNextIterator is used only in HbvNext and that function is never used

Commit migrated from https://github.com/dotnet/coreclr/commit/235bc725acdf8a66b19f1c51cfe83f573562f80d