[clang][dataflow] Remove a redundant trailing semicolon. NFC.

This silences the following warning with GCC:

    llvm-project/llvm/tools/clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp:89:4: warning: extra ‘;’ [-Wpedantic]
       89 |   };
          |    ^
          |    -