docs: don't say that data flow tracing interface is unstable

[dvyukov]

Summary

We are starting to use data flow tracing in kernel.
The interface is not subject to change anymore.

[kcc]

LGTM,
although this will not prevent us from changing the interface in future :)

docs/SanitizerCoverage.rst

.. code-block:: c++
   // Val is the second argument of division.
   void __sanitizer_cov_trace_div4(uint32_t Val);
   void __sanitizer_cov_trace_div8(uint64_t Val);
 
   // Called before a GetElemementPtr (GEP) instruction
   // for every non-constant array index.
   void __sanitizer_cov_trace_gep(uintptr_t Idx);
 
-This interface is a subject to change.
-
 Default implementation
 ======================
 
 The sanitizer run-time (AddressSanitizer, MemorySanitizer, etc) provide a
 default implementations of some of the coverage callbacks.
 You may use this implementation to dump the coverage on disk at the process
 exit.