Administration: Reverse the arrow direction for database import/export icons.

In [48456], database import and export icons were introduced. However, the arrows were pointing in the wrong directions. This reverses the arrows to be pointing correctly based on the action described in the name.

Props johnbillion, joen, desrosj, empireoflight.
Fixes #49913.
Built from https://develop.svn.wordpress.org/trunk@48506


git-svn-id: https://core.svn.wordpress.org/trunk@48268 1a063a9b-81f0-0310-95a4-ce76da25c4cd