DO NOT MERGE AppSecurity run on current user.

AppSecurityPreparer - Do not try to remove user if it is the current user. This avoids an unhelpful error message when deleting the current user fails.
BaseAppSecurityTest - Do not switch to primary user. Also, remove check for split system user which is never used by a test.
DirectBootHostTest - Run tests as current user. Running on multiple users never happens since prepareSingleUser always returns a single user.
InstantAppUserTest - Switch back to the user that was used before the test began.
PackageResolutionHostTest - call super.setup since overriding the method means that BaseAppSecurityTest@setupUp is not called.
PermissionsHostTest - Run tests as current user.
Utils - Don't bother stopping the current user. This removes an unhelpful warning message.

bug: 117880211
Test:  $ cts-tradefed run cts-dev -a arm64-v8a -m CtsAppSecurityHostTestCases
On a prod PI phone and device in a secondary user.

Change-Id: Ibc010d74567830ed4ca4a2a153965deae62d60e4