[rocprof-sys] Use fmt APIs to construct strings instead of JOIN (#2643)

## Motivation

With the introduction of the new logging system base on `spdlog` library, opportunity shows to replace `timemory` dependent JOIN implementation with `fmt` library `format` and `join` APIs, which are shipped as a part of `spdlog` lib

## Technical Details

Use `fmt` provided APIs to properly format and package strings.

projects/rocprofiler-systems/source/lib/core/mproc.cpp

@@ -43,7 +43,7 @@ get_concurrent_processes(int _ppid)
     std::set<int> _children = {};
     if(_ppid > 0)
     {
-        auto          _inp = JOIN('/', "/proc", _ppid, "task", _ppid, "children");
+        auto          _inp = fmt::format("/proc/{}/task/{}/children", _ppid, _ppid);
         std::ifstream _ifs{ _inp };
         if(!_ifs)
         {