This commit fixes the path listed in the documentation for the fuzz
testing test_runner.py. Previously the --help option worked but running
fuzz tests from the documented path did not.
There turned out to be a mismatch in the tx output counts which caused
'ConnectBlockMixedEcdsaSchnorr' benchmark to run slower than
'ConnectBlockAllEcdsa' and 'ConnectBlockAllSchnorr'. This commit makes
the tx output counts uniform across all benchmarks.
This commit also renames the 'taproot_tx' variable to 'tx' to reflect
that this variable represents a general tx and not just a taproot tx.