Fix drive mounted directory on Windows

On my Windows machine, I mount drive D: to the directory C:\src.

The old implementation returns the incorrect 'C:\\??\\Volume{ad2eb15e-f293-4d48-a448-54757d95a97c}' result, which breaks the repo init command.

With the use of os.path.realpath, it can return 'D:\\' correctly.

Change-Id: Ia5f53989055125cb282d4123cf55d060718aa1ff
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/416580
Reviewed-by: Greg Edelston <gredelston@google.com>
Tested-by: Kaiyi Li <kaiyili@google.com>
Commit-Queue: Kaiyi Li <kaiyili@google.com>

platform_utils.py

@@ -259,24 +259,4 @@ def realpath(path):
 
     Availability: Windows, Unix.
     """
-    if isWindows():
-        current_path = os.path.abspath(path)
-        path_tail = []
-        for c in range(0, 100):  # Avoid cycles
-            if islink(current_path):
-                target = readlink(current_path)
-                current_path = os.path.join(
-                    os.path.dirname(current_path), target
-                )
-            else:
-                basename = os.path.basename(current_path)
-                if basename == "":
-                    path_tail.append(current_path)
-                    break
-                path_tail.append(basename)
-                current_path = os.path.dirname(current_path)
-        path_tail.reverse()
-        result = os.path.normpath(os.path.join(*path_tail))
-        return result
-    else:
     return os.path.realpath(path)