refactor: refine timestamp expr function

[zhaoyongjie]

SUMMARY

refactor timestamp expression function, the original interface of the function has to point out the type of column, the type_ argument is redundant.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Pure backend change

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #21510 (9883d9f) into master (fdb4702) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master   #21510   +/-   ##
=======================================
  Coverage   66.67%   66.67%           
=======================================
  Files        1793     1793           
  Lines       68493    68494    +1     
  Branches     7275     7275           
=======================================
+ Hits        45665    45666    +1     
  Misses      20966    20966           
  Partials     1862     1862           

Flag	Coverage Δ
hive	53.08% <0.00%> (-0.01%)	⬇️
mysql	78.20% <100.00%> (+<0.01%)	⬆️
postgres	78.27% <100.00%> (+<0.01%)	⬆️
presto	52.98% <0.00%> (-0.01%)	⬇️
python	81.41% <100.00%> (+<0.01%)	⬆️
sqlite	76.76% <100.00%> (+<0.01%)	⬆️
unit	51.06% <50.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/db_engine_specs/pinot.py	97.36% <ø> (ø)
superset/connectors/sqla/models.py	90.60% <100.00%> (ø)
superset/db_engine_specs/base.py	89.58% <100.00%> (+0.01%)	⬆️

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[villebro]

LGTM, thanks for cleaning this up!