6/ Update pip to use shell main thread

- Remove some currently unused pip interface methods
- Remove some usages of handler
- Remove update thread (will eventually run on shell main thread)

Bug: 161979899
Test: atest WMShellUnitTests
Change-Id: If97e5182e396029120f0d0fb9e730ece93cddcc8
Signed-off-by: Winson Chung <winsonc@google.com>
27 files changed