fix interpreting int as second--> nano

[jbrockmendel]

The existing behavior was put in place in #4684, looks like wrestling with numpy 1.6 and 1.7 was rough.

Not sure what this merits in the whatsnew, pls advise.

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

[jbrockmendel]

Travis fail is hypothesis

[jbrockmendel]

Closes #19233

[codecov]

Codecov Report

Merging #24694 into master will increase coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master   #24694      +/-   ##
==========================================
+ Coverage   43.06%   43.06%   +<.01%     
==========================================
  Files         166      166              
  Lines       52310    52310              
==========================================
+ Hits        22526    22529       +3     
+ Misses      29784    29781       -3

Flag	Coverage Δ
#single	43.06% <0%> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/core/internals/blocks.py	52.71% <0%> (ø)	⬆️
pandas/util/testing.py	50.73% <0%> (-0.93%)	⬇️
pandas/io/json/json.py	62.85% <0%> (+1.19%)	⬆️
pandas/core/internals/construction.py	64.21% <0%> (+2.03%)	⬆️

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[codecov]

Codecov Report

Merging #24694 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #24694      +/-   ##
==========================================
+ Coverage   92.38%   92.38%   +<.01%     
==========================================
  Files         166      166              
  Lines       52310    52311       +1     
==========================================
+ Hits        48327    48328       +1     
  Misses       3983     3983

Flag	Coverage Δ
#multiple	90.8% <100%> (ø)	⬆️
#single	43.06% <0%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/internals/blocks.py	94.31% <100%> (ø)	⬆️

---

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[jbrockmendel]

Reverted change, made a deprecation instead.

[jreback]

lgtm. ping on green.