[llvm][vfs] Remove blank comment after \endverbatim doxygen command (#83240)

Blank comment line afer \endverbatim malfunctions the doxygen parser.
  Check the "Detailed Description" section on
https://llvm.org/doxygen/classllvm_1_1vfs_1_1RedirectingFileSystem.html


Screenshot is attached below


![image](https://github.com/llvm/llvm-project/assets/22870466/35fc2444-d2f4-4638-990e-241cc14d0986)