Do not keep the input array with CPU times

CpuTimePerUidFreq puller kept the input array with CPU times to avoid
copies, but that array is owned by the reader and is mutated for each
callback invocation. This corrupted the aggregated data.

Bug: 157535126
Test: cmd stats pull-source 10010
Test: atest CpuStatsTests
Change-Id: Icda6a71f558e582c5d5b497e2cca1d84deed8b99
Merged-In: Icda6a71f558e582c5d5b497e2cca1d84deed8b99