Fixed #19638 -- Skipped tx support testing for some DBs

PostgreSQL and Oracle always support transactions, so the create table
and rollback test is non-necessary on those DBs.

Thanks to shai for report.
Fixed #19720 -- Oracle ordering related delete regression

When a query had a complex where condition (a condition targeting more
than the base table) a subquery was used for deletion. However, the
query had default ordering from the model's meta and Oracle doesn't
work with ordered subqueries.

The regression was caused by fast-path deletion code introduced in
1cd6e04cd4f768bcd4385b75de433d497d938f82 for fixing #18676.

Thanks to Dylan Klomparens for the report.
Added a note about the default timezone and the new project template.

Thanks JonLoy for the draft patch.
Made Query.clear_ordering force_empty arg mandatory

Previously it was possible to call clear_ordering without the
force_empty argument. The result was that the query was still ordered
by model's meta ordering if that was defined. By making the arg
mandatory it will be easier to spot possible errors caused by assuming
clear_ordering will remove all ordering.

Thanks to Dylan Klomparens for the suggestion. Refs #19720.
Fixed #19112 -- Reduced the amount of query params in a test
Emphasized MyISAM pseudo-requirement for GeoDjango over MySQL

Refs #15295.