Simplify user ID retrieval in UserManagerServiceMockedTest#testAutoLock*

To get user ID from UserInfo, these tests are converting it into
UserHandle. Simplify it by accessing UserInfo#id (public member)
directly.

Bug: 411222385
Test: atest FrameworksMockingServicesTests:UserManagerServiceMockedTest
Flag: TEST_ONLY

Change-Id: I2dd4a91d75d14a53562482df8ec10618f8754514