[clang][dataflow] Remove unnecessary `ASTContext` parameter from...

[clang][dataflow] Remove unnecessary `ASTContext` parameter from `ControlFlowContext::build` overload.

When introducing this new overload in https://reviews.llvm.org/D151183, I didn't consider that the `ASTContext` parameter was unnecessary because it could also be obtained from the `FunctionDecl`.

Reviewed By: gribozavr2, xazax.hun

Differential Revision: https://reviews.llvm.org/D151549