### What changes were proposed in this pull request?
Extracting millennium, century, decade, millisecond, microsecond and epoch from datetime is neither ANSI standard nor quite common in modern SQL platforms. Most of the systems listing below does not support these except PostgreSQL and redshift.
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDFhttps://docs.oracle.com/cd/B19306_01/server.102/b14200/functions050.htmhttps://prestodb.io/docs/current/functions/datetime.htmlhttps://docs.cloudera.com/documentation/enterprise/5-8-x/topics/impala_datetime_functions.htmlhttps://docs.snowflake.com/en/sql-reference/functions-date-time.html#label-supported-date-time-partshttps://www.postgresql.org/docs/9.1/functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT
This PR removes these extract fields support from extract function for date and timestamp values
`isoyear` is PostgreSQL specific but `yearofweek` is more commonly used across platforms
`isodow` is PostgreSQL specific but `iso` as a suffix is more commonly used across platforms so, `dow_iso` and `dayofweek_iso` is used to replace it.
For historical reasons, we have [`dayofweek`, `dow`] implemented for representing a non-ISO day-of-week and a newly added `isodow` from PostgreSQL for ISO day-of-week. Many other systems only have one week-numbering system support and use either full names or abbreviations. Things in spark become a little bit complicated.
1. because of the existence of `isodow`, so we need to add iso-prefix to `dayofweek` to make a pair for it too. [`dayofweek`, `isodayofweek`, `dow` and `isodow`]
2. because there are rare `iso`-prefixed systems and more systems choose `iso`-suffixed way, so we may result in [`dayofweek`, `dayofweekiso`, `dow`, `dowiso`]
3. `dayofweekiso` looks nice and has use cases in the platforms listed above, e.g. snowflake, but `dowiso` looks weird and no use cases found.
4. with a discussion the community，we have agreed with an underscore before `iso` may look much better because `isodow` is new and there is no standard for `iso` kind of things, so this may be good for us to make it simple and clear for end-users if they are well documented too.
Thus, we finally result in [`dayofweek`, `dow`] for Non-ISO day-of-week system and [`dayofweek_iso`, `dow_iso`] for ISO system
### Why are the changes needed?
Remove some nonstandard and uncommon features as we can add them back if necessary
### Does this PR introduce any user-facing change?
NO, we should target this to 3.0.0 and these are added during 3.0.0
### How was this patch tested?
Remove unused tests
Closes#28284 from yaooqinn/SPARK-31507.
Authored-by: Kent Yao <yaooqinn@hotmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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