[Clean up] remove unused private member of FindbarView

|preferred_height_| isn't no longer used. This CL is for cleaning up.

Bug: none
Change-Id: I8c82e540c90bed5101fb2fcb07c06c70824177b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2257088
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780784}

chrome/browser/ui/views/find_bar_view.h

@@ -114,9 +114,6 @@ class FindBarView : public views::View,
   views::ImageButton* find_next_button_;
   views::ImageButton* close_button_;
 
-  // The preferred height of the find bar.
-  int preferred_height_;
-
   DISALLOW_COPY_AND_ASSIGN(FindBarView);
 };