Removing non SYSTEM user before running systemUserOnlyTest

Bug: 295446676
Test: atest UserManagerServiceTest -c
Change-Id: I6f536b7f5b85e4e884bd284b1848e43ac3c9029d
(cherry picked from commit b1bba3e972890edfdb33b063e741baa6745f5283)
Merged-In: I6f536b7f5b85e4e884bd284b1848e43ac3c9029d
1 file changed