layouts: Fill some placeholders with '²' and '³'

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/703>

data/keyboards/si_wide.yaml

@@ -23,13 +23,13 @@ views:
         - "show_upper Y X C V B N M -- BackSpace"
         - "show_numbers show_upper_accents preferences space ! ? Return"
     numbers:
-        - "1 2 3 4 5 6 7 8 9 0"
-        - "@ # $ % & - _ + ( )"
+        - "1 2 3 4 5 6 7 8 9 0 ²"
+        - "@ # $ % & - _ + ( ) ³"
         - "show_symbols , \" ' : ; ! ? -- BackSpace"
         - "show_letters show_accents preferences space , . Return"
     symbols:
-        - "~ ` | · √ π τ ÷ × ¶"
-        - "© ® £ € ¥ ^ ° * { }"
+        - "~ ` | · √ π τ ÷ × ¶ ²"
+        - "© ® £ € ¥ ^ ° * { } ³"
         - "show_numbers \\ / < > = [ ] -- BackSpace"
         - "show_letters show_accents preferences space § ¤ Return"
     accents:
@@ -137,17 +137,9 @@ buttons:
         text: "Đ"
     5:
         outline: "fill"
-    6:
-        outline: "fill"
     "&":
         outline: "fill"
-    -:
-        outline: "fill"
     √:
         outline: "fill"
-    π:
-        outline: "fill"
     ¥:
         outline: "fill"
-    ^:
-        outline: "fill"