Change Details

``` The first commit improves documentation on setup_clean_chain which is misunderstood quite frequently. Most importantly it fixes the TestShell docs which are simply incorrect. The second commit removes the instances of setup_clean_clain in functional tests where it is not changing the default. ``` Backport of core#21042.

``` The first commit improves documentation on setup_clean_chain which is misunderstood quite frequently. Most importantly it fixes the TestShell docs which are simply incorrect. The second commit removes the instances of setup_clean_clain in functional tests where it is not changing the default. ``` Backport of [[https://github.com/bitcoin/bitcoin/pull/21042 | core#21042]].

``` The first commit improves documentation on setup_clean_chain which is misunderstood quite frequently. Most importantly it fixes the TestShell docs which are simply incorrect. The second commit removes the instances of setup_clean_clain in functional tests where it is not changing the default. ``` Backport of [[https://github.com/bitcoin/bitcoin/pull/21042 | core#21042]].