Clear old custom name formats when database loaded

[Nick-Hall]

No description provided.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (maintenance/gramps50@8959254). Click here to learn what that means.
The diff coverage is 100%.

@@                   Coverage Diff                   @@
##             maintenance/gramps50     #509   +/-   ##
=======================================================
  Coverage                        ?   42.52%           
=======================================================
  Files                           ?     1059           
  Lines                           ?   141361           
  Branches                        ?        0           
=======================================================
  Hits                            ?    60110           
  Misses                          ?    81251           
  Partials                        ?        0

Impacted Files	Coverage Δ
gramps/gen/display/name.py	57.1% <100%> (ø)
gramps/cli/grampscli.py	53.44% <100%> (ø)

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