Update Clang-REPL docs with removing the redundant subsections

[Krishna-13-cyber]

Summary

The Clang documentation is currently displaying 3 subsections for the same Clang-REPL docs instead of one subsection.
This patch fixes the above problem and displays just one subsection for Clang-REPL under the section of Using Clang Tools

[v.g.vassilev]

LGTM!

clang/docs/ClangRepl.rst

6. The LLVM IR is the input format for LLVM’s JIT compilation infrastructure.
    The tool will instruct the JIT to run specified functions, translating them
    into machine code targeting the underlying device architecture (eg. Intel
    x86 or NVPTX).
 
 7. The LLVM JIT lowers the LLVM IR to machine code.
 
 8. The machine code is then executed.
 
-===================
 Build Instructions:
 ===================
 
 
 .. code-block:: console
 
    $ cd llvm-project
    $ mkdir build

 **Clang-repl** is built under llvm-project/build/bin. Proceed into the directory **llvm-project/build/bin**
 
 .. code-block:: console
 
    ./clang-repl
    clang-repl>
 
 
-================
 Clang-Repl Usage
 ================
 
 **Clang-Repl** is an interactive C++ interpreter that allows for incremental
 compilation. It supports interactive programming for C++ in a
 read-evaluate-print-loop (REPL) style. It uses Clang as a library to compile the
 high level programming language into LLVM IR. Then the LLVM IR is executed by
 the LLVM just-in-time (JIT) infrastructure.