[LLDB] Remove uneeded CopyType from BlockPointerSyntheticFrontEnd

BlockPointerSyntheticFrontEnd does a CopyType which results in it copying the type
back into its own context. This will result in a call to ASTImporterDelegate::setOrigin
with &decl->getASTContext() == origin.ctx this can result in an infinite recursion
later on in ASTImporter since it will attempt to find the decl in its origin which will be itself.

Differential Revision: https://reviews.llvm.org/D96366