os: remove 5ms sleep on Windows in (*Process).Wait
The 5ms sleep in (*Process).Wait was added to mitigate errors while
removing executable files using os.RemoveAll.
Windows 10 1903 implements POSIX semantics for DeleteFile, making the
implementation of os.RemoveAll on Windows much more robust. Older
Windows 10 versions also made internal improvements to avoid errors
when removing files, making it less likely that the 5ms sleep is
necessary.
Windows 10 is the oldest version that Go supports (see #57004), so it
makes sense to unconditionally remove the 5ms sleep now. We have all
the Go 1.22 development cycle to see if this causes any regression.