The unused includes where found by applying this scripted diff which removes the chainparamsbase header in all files where it is included, but not used. This is done by filtering against all defined symbols of the header as well as its respective .cpp file.
sed -i '/#include <chainparamsbase.h>/d' $( git grep -l 'chainparamsbase.h' | xargs grep -L 'CBaseChainParams\|CreateBaseChainParams\|SetupChainParamsBaseOptions\|BaseParams\|SelectBaseParams\|chainparamsbase.cpp' )
Then the #include was added where it was actually missing and was previously included indirectly.
This concludes backport of core#27491
https://github.com/bitcoin/bitcoin/pull/27491/commits/e9ee8aaf3acdf6dce2b339916d4c602484570050
https://github.com/bitcoin/bitcoin/pull/27491/commits/d168458d1ff987e0d741c75ac1d4b63ae0cfb7e7
Depends on D17988