Remove gpumemtracer bloat

The size of gpuservice regressed while adding perfetto trace functions
inside GpuMemTracer for unittests. This change fixes the regression by
moving readPackets into the unittest, thereby removing the need to
include some libraries in gpumemtracer.so

Bug: 175904796
Test: atest gpuservice_unittest:GpuMemTracerTest
Change-Id: Ifaafdbfb24f8c51712276ef7efd645ce43c987f4
Merged-In: Ifaafdbfb24f8c51712276ef7efd645ce43c987f4