table map consulted during setup fields on unfixed items

For the 2nd execution of a prepared statement, setup_fields can query the table map of items not yet (re)fixed. This is evident in a number of .rdiff files in our test suite.
We can fix this by relaxing some assert behaviour in the fixing process and calling item->update_used_tables() before the above happens.
We can then remove the relevant .rdiff files.

Split from MDEV-35673