The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

The DynamicFifoBuffer methods never return nullptr when the buffer is
empty or full; instead, they return an empty buffer.  This bug caused
an endless loop.

Switch to the C++ version.