simpleperf: remove some deprecated code.

Remove perf_clock.cpp. perf_clock.cpp was used to drop samples generated
while dumping thread maps in system wide recording. But that strategy isn't
useful and has been removed.
Remove SampleRecord::RemoveInvalidStackData().
Simplify SampleRecord::GetValidStackSize().

Bug: 110174247
Test: run simpleperf_unit_test.
Change-Id: Ie934c8ecf5d57147b163e490368e71716da45258
7 files changed