stbt.android: Don't import stbt unless we need to
stbt.android: Don't import stbt unless we need to

If you're only going to use `AdbDevice.press` then there's no need to
load all of stbt's dependencies. This improves the startup time of
`stbt-control` noticeably (several seconds).

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester