ACK ef97b89
Tested that the patch does eliminate the logging lines quoted in the description. I think this is a useful change because those log entries add little to no value. Eliminating them makes the logs easier to read when writing or understanding functional tests (I do this often myself).

ACK ef97b89, confirmed that this log level is only used in random.cpp and indeed it seems that it doesn't add any value to the debug.log during functional tests.

ACK ef97b89

Confirmed what kouloumos said about this log level only appearing in random.cpp:

grep -r -i --color='always' 'BCLog::RAND' .
./bitcoin/src/logging.cpp:    {BCLog::RAND, "rand"},
./bitcoin/src/random.cpp:    LogPrint(BCLog::RAND, "Feeding %i bytes of dynamic environment data into RNG\n", hasher.Size() - old_size);
./bitcoin/src/random.cpp:    LogPrint(BCLog::RAND, "Feeding %i bytes of environment data into RNG\n", hasher.Size() - old_size);

Applied the code change an observed that the rand debug logs are no longer appearing for bitcoind instances that the functional tests start up. Suppressing them feels like a good idea because it makes the debug logs easier to read. The likelihood that someone needs these log statements for testing is very small compared to the amount of the tests where these log messages are just noise.

Thanks for all the quick feedback, and thanks for the warm welcome @theStack!