autoninja.bat: fix comment about vpython

We use vpython3 in autoninja.bat now.

Current difference of python3 and vpython3 for autoninja.py invocation
is like belows and I think several hundred milliseconds is acceptable
increase for the build.

gLinux:
* vpython3: 240.0ms
* python3:   99.1ms
https://pastebin.com/LK8kUAHn

gWindows:
* vpython3: 912.7ms
* python3:  611.8ms
https://pastebin.com/Xqs77ipv

MacBook Pro:
* vpython3: 386.2ms
* python3:  280.1ms
https://pastebin.com/eyXEpM7Q

Bug: 327625559
Change-Id: Iff52be12cb755b3ecdab6663a0038905cf178d53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5348020
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>

autoninja.bat

@@ -25,7 +25,6 @@ if not defined AUTONINJA_BUILD_ID (
 if "%NINJA_SUMMARIZE_BUILD%" == "1" set "NINJA_STATUS=[%%r processes, %%f/%%t @ %%o/s : %%es ] "
 
 :: Execute autoninja.py and pass all arguments to it.
-:: Don't use vpython - it is too slow to start.
 :: Don't use python3 because it doesn't work in git bash on Windows and we
 :: should be consistent between autoninja.bat and the autoninja script used by
 :: git bash.