Make --allow-redefinition mean --allow-redefinition-new (#21276)
Also now `--allow-redefinition` is the primary flag name for the
previous `--allow-redefinition-new` flag, and the
`--allow-redefinition-new` name is a (soft deprecated) alias.
The original `--allow-redefinition` behavior is still available via
`--allow-redefinition-old`.
Also removed some now redundant `--local-partial-types` flags in tests.
