Add description for c21060, itemized deductions before phase-out

[martinholmer]

Add another description to the records_variables.json file.

[martinholmer]

How can it be that adding a few characters to a documentation string in the records_variables.json file causes a test failure under Python 3.4 (even though there are no test failures under Python 2.7 and Python 3.5)?

[codecov-io]

Codecov Report

Merging #1307 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1307   +/-   ##
=======================================
  Coverage   99.65%   99.65%           
=======================================
  Files          38       38           
  Lines        2878     2878           
=======================================
  Hits         2868     2868           
  Misses         10       10

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