Fix kdeconnect-symbolic icons not being able to switch colors while generating their breeze-dark version

This patch just touches the kdeconnect-symbolic icons color properties so they become completely homogeneous and on par of their neighbor icons.

This makes it actually respect the color scheme so it doesn't stay completely black while generating their breeze-dark version, and also makes it look not pitch-black so it plays nicely with other icons even on breeze light.