simpleperf: dump only needed symbols in file feature section.

simpleperf: dump only needed symbols in file feature section.

Instead of dumping all symbols in the hit elf files, dump only
needed symbols can save a lot of space. To do so, read perf.data
after recording to collect hit file and symbol information.

Bug: http://b/32340274
Test: test using `simpleperf record --dump-symbols` manually.
Test: run simpleperf_unit_test.
Change-Id: I480f3e2e7ccebfbb5df16a597724f5f40d62c821