Simplify handleStartCopy method so that it is easier to understand

- We only enable rollback when INSTALL_ENABLE_ROLLBACK is set, which is
never true when we are moving package.
- installLocationPolicy doesn't return RECOMMEND_INSTALL_EPHEMERAL, so
we can skip setting INSTALL_INSTANT_APP flag on installFlags.

Bug: 136257624
Test: atest GtsSecurityHostTestCases
Test: atest CtsAtomicInstallTestCases
Change-Id: I7c64fd19b1824694d30e00e8fb573cf50077dec3