[com.google.fonts/check/whitespace_glyphs] rationale recommends U+00AD SOFT HYPHEN, but other checks recommend against it

[drj11]

Observed behaviour

When com.google.fonts/check/whitespace_glyphs fails, the rationale text is:

The OpenType specification recommends that fonts should contain glyphs for  
the following whitespace characters:                                        
                                                                            
- U+0020 SPACE - U+00A0 NO-BREAK SPACE                                      
                                                                            
The space character is required for text processing, and the no-break       
space is useful to prevent line breaks at its position. It is also          
recommended to have a glyph for the tab character (U+0009) and the soft     
hyphen (U+00AD), but these are not mandatory.

This issue concerns U+00AD SOFT HYPHEN; the text of this rationale recommends having a glyph for U+00AD SOFT HYPHEN, but other checks and discussions recommend against including such a glyph.

See com.google.fonts/check/soft_hyphen

(Describe the results you're getting)

Expected behaviour

Avoid mentioning U+00AD SOFT HYPHEN in the rationale of this check at all.

(though i note #4095 has resulted in the rationale for com.google.fonts/check/soft_hyphen changing, that issue has not been closed)

Maybe we should also look into U+0009 CHARACTER TABULATION (from Unicode 1.0); i have no idea.

Resources and steps needed to reproduce

For example, remove /uni00A0 from a font and run fontbakery.