Change Perfetto Source to Github (#373)

- Current Perfetto source repo is from android.googlesource
        which is censored in China and causes an infinite
        hang when building Omnitrace
- This commit changes the Perfetto source repo to Github which acts
        as a read-only mirror to the googlesource perfetto
        repo.

Co-authored-by: David Galiffi <David.Galiffi@amd.com>

[ROCm/rocprofiler-systems commit: 6f22b2d2e5]

projects/rocprofiler-systems/.gitmodules

@@ -3,7 +3,7 @@
 	url = https://github.com/NERSC/timemory.git
 [submodule "external/perfetto"]
 	path = external/perfetto
-	url = https://android.googlesource.com/platform/external/perfetto
+	url = https://github.com/google/perfetto.git
 [submodule "external/elfio"]
 	path = external/elfio
 	url = https://github.com/jrmadsen/ELFIO.git