Improve tc CLI docs about when extrapolation takes place

[MattHJensen]

Resolves #2384 (cc @donboyd5).

• adds a paragraph to the uguide about how your data filename influences extrapolation.
• increases the specificity of the reform documentation .text file so that it does not tell the user that default growth assumptions have been applied even when no extrapolation took place.
• adds a new message on startup when data are not extrapolated to accompany the message offered when data are extrapolated.
  

This PR also updates the results -- minor changes -- for reform 56, which repeals the TCJA CPI adjustment. I am assuming that these changes are a result of #2388 and were just overlooked in testing as they raise an error and not a test failure. (cc @MaxGhenis).

[codecov]

Codecov Report

Merging #2394 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #2394   +/-   ##
======================================
  Coverage     100%    100%           
======================================
  Files          13      13           
  Lines        2749    2751    +2     
======================================
+ Hits         2749    2751    +2

Impacted Files	Coverage Δ
taxcalc/calculator.py	100% <100%> (ø)	⬆️

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