Remove custom arrow indicator in Select dropdown fields
Summary:
Use default browser arrow, unless someone has strong opinions.
Refs T15056
Test Plan: Go to a Maniphest task or Differential revision, in Default mode and Dark mode, and look at the "Add Action..." dropdown.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15056
Differential Revision: https://we.phorge.it/D26665