Don't limit Windows USB reads.

In 3d2904cd we removed the code that broke
Linux USB reads into 4KiB chunks. This patch does the same for Windows. This
improves Windows "adb pull" speeds 6x in my VM. (There was no equivalent
problem with writes, so this change only affects pull speeds.)

Change-Id: If19013e5f51975f4824bf9147b7b76cebd305b96