use Timedelta instead of convert_to_timedelta64

[jbrockmendel]

• closes #xxxx
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[codecov]

Codecov Report

Merging #24821 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #24821      +/-   ##
==========================================
- Coverage   92.38%   92.38%   -0.01%     
==========================================
  Files         166      166              
  Lines       52379    52378       -1     
==========================================
- Hits        48392    48390       -2     
- Misses       3987     3988       +1

Flag	Coverage Δ
#multiple	90.81% <100%> (-0.01%)	⬇️
#single	42.91% <25%> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/core/tools/timedeltas.py	98% <100%> (-0.04%)	⬇️
pandas/util/testing.py	88.04% <0%> (-0.1%)	⬇️

---

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[codecov]

Codecov Report

Merging #24821 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #24821      +/-   ##
==========================================
- Coverage   92.38%   92.38%   -0.01%     
==========================================
  Files         166      166              
  Lines       52379    52378       -1     
==========================================
- Hits        48392    48391       -1     
  Misses       3987     3987

Flag	Coverage Δ
#multiple	90.81% <100%> (-0.01%)	⬇️
#single	42.91% <25%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/tools/timedeltas.py	98% <100%> (-0.04%)	⬇️

---

Continue to review full report at Codecov.

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2bbe418...8c6d63e. Read the comment docs.

[jreback]

prob can now change convert_to_timedelta64 to cdef from cpdef

[jbrockmendel]

prob can now change convert_to_timedelta64 to cdef from cpdef

Good idea. Also removed some util.is_array checks that can never be True.

[jreback]

thanks!