Remove string frees to support GetUTFRegion transition

Removed string free calls from tracing SDK now obsolete with
the move from GetUTFStringChars to GetUTFRegion in the JNI
string handling.

The higher level code (JNI) never owns memory unless it's
explicitly copied into a string for instance. This makes
memory management simpler and provides some performance
opportunities in the caller.

Test: atest PerfettoTest
Bug: 303199244
Flag: android.os.perfetto_sdk_tracing_v2
Change-Id: I495cd593f04e7444527b567bc7efddfe0cd92f71