Rename HAVE_DISPLAY_FAST_MODE define

[abonnaudet-ledger]

HAVE_DISPLAY_FAST_MODE define collided with a define on OS side.

Changes include

• Bugfix (non-breaking change that solves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• Documentation
• Other (for changes that might not fit in any category)

Breaking changes

Please complete this section if any breaking changes have been made, otherwise delete it.

Additional comments

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.54%. Comparing base (cc14f18) to head (8d1d7e9).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #684   +/-   ##
=======================================
  Coverage   60.54%   60.54%           
=======================================
  Files          12       12           
  Lines        1726     1726           
=======================================
  Hits         1045     1045           
  Misses        681      681           

Flag	Coverage Δ
unittests	60.54% <ø> (ø)

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