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7507caf944f8eb98e55730e60e77f9060c572788 by Derek Mauro <dmauro@google.com>:

Remove RunningOnValgrind() and ValgrindSlowdown() from dynamic_annotations.h

These are defined by some sanitizer implementations and possibly Valgrind.
Abseil decided to define them when the implementation was unavailable so
that they could be unconditionally called, but we now consider this a mistake.
Other libraries, including Python, have copied this method, leading to
multiple definitions when these libraries are used together.

In the unlikely case that code is using Abseil's definition, it
is recommended that the call be guarded instead:
```
#if __has_feature(thread_sanitizer)
extern "C" int RunningOnValgrind();
if (RunningOnValgrind()) ...
#endif
```

Fixes #1011

PiperOrigin-RevId: 394501460
GitOrigin-RevId: 7507caf944f8eb98e55730e60e77f9060c572788
Change-Id: I5ddaf9a590c857d645461352a0f6fbccbb3d5584