When commit 961fdd861fac46ef0ecc67bb8be14c0ce828e612 landed
text in the overview search entry field started getting clipped.
This is because the default font size changed but the entry is a
hard coded pixel height.
This commit drops the hard coding, so the entry can automatically
size itself to the proper height.
https://bugzilla.gnome.org/show_bug.cgi?id=641537