Relax the lock in getMemoryStateForProcesses

Metrics need to be pulled in time while the lock could delay that.
The oom adj score in the returned data set could be inconsitent
from the actual one but other data fields are not and it's preferrable
to pull them.

Bug: 192440905
Test: atest CtsStatsdAtomHostTestCases:ProcessMemoryStatsTests
Change-Id: I055b8baa87d53114de51b65e3f483635441e5ddc