Clean up layout-files

- Change text to symbols
- Remove unused button-definitions

This makes these layout-files easier to understand and edit.

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/629>

data/keyboards/bg.yaml

@@ -20,7 +20,7 @@ views:
     numbers:
         - "1 2 3 4 5 6 7 8 9 0"
         - "@ # € % & - _ + ( )"
-        - "show_symbols , \" ' colon ; ! ? ѝ BackSpace"
+        - "show_symbols , \" ' : ; ! ? ѝ BackSpace"
         - "show_letters preferences         space        Return"
     symbols:
         - "~ ` | · √ π τ ÷ × ¶"
@@ -72,7 +72,3 @@ buttons:
         outline: "wide"
         icon: "key-enter"
         keysym: "Return"
-    colon:
-        text: ":"
-    "\"":
-        keysym: "quotedbl"