ONS: remove ONSStatsInfo.mIsProvisioningResultUpdated which is redundant

mIsProvisioningResultUpdated is completely redundant info. It can always
replaced by checking if mProvisioningResult is null.

Bug: 240081918
Test: atest ONSTests
Flag: EXEMPT (non-functional change)
Change-Id: If2ad837024da47b06de999232cfd8ab2a6073693