[build] Remove Windows constexpr mutex define (#7375)

Since we ship a newer runtime, and we also have checks to ensure a valid runtime, we can remove this again.

cmake/modules/CompileWarnings.cmake

@@ -55,9 +55,4 @@ macro(wpilib_target_warnings target)
     )
         target_compile_options(${target} PRIVATE -gz=zlib)
     endif()
-
-    # Disable std::mutex constexpr constructor on MSVC
-    if(MSVC)
-        target_compile_options(${target} PRIVATE /D_DISABLE_CONSTEXPR_MUTEX_CONSTRUCTOR)
-    endif()
 endmacro()