Do not access SettingProvider in test code

New policy: b/175024829
Settings key: <one_handed_*> is not readable.
From S+, new public settings keys need to be annotated
with @Readable unless they are annotated with @hide.

Recent changes :
ag/13764747 Remove @Readable for hidden fields added in S

Test: atest WMShellUnitTests
Bug: 183064974
Change-Id: I185491189a3804d7038be3c117583ab571e7a961