Layouts: Optimise the size of some buttons on some layouts

and clean up some layout-files.

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/655>

data/keyboards/cz.yaml

@@ -7,7 +7,6 @@ outlines:
     spaceline:     { width: 106,   height: 52 }
     special:       { width: 35.33, height: 52 }
     change-view-2: { width: 35.33, height: 52 }
-    placeholder:   { width: 35.33, height: 52 }
 
 views:
     base:
@@ -100,6 +99,3 @@ buttons:
         outline: "wide"
         icon: "key-enter"
         keysym: "Return"
-    --:
-        outline: "placeholder"
-        text: ""