Remove some semicolons

Remove semicolons everywhere except 'using' statements, properties,
attributes, and signals.

This should be the last breaking change to the syntax.

gtkblueprinttool/extensions/gtk_combo_box_text.py

@@ -65,7 +65,7 @@ item = Group(
 
 items = Group(
     Items,
-    Statement(
+    Sequence(
         Keyword("items", True),
         OpenBracket(),
         Delimited(

gtkblueprinttool/extensions/gtk_file_filter.py

@@ -49,7 +49,7 @@ class FilterString(AstNode):
 def create_node(tag_name: str, singular: str):
     return Group(
         Filters,
-        Statement(
+        Sequence(
             Keyword(tag_name, True),
             UseLiteral("tag_name", tag_name),
             OpenBracket(),

gtkblueprinttool/extensions/gtk_size_group.py

@@ -60,7 +60,7 @@ class Widget(AstNode):
 
 widgets = Group(
     Widgets,
-    Statement(
+    Sequence(
         Keyword("widgets", True),
         OpenBracket(),
         Delimited(

gtkblueprinttool/extensions/gtk_string_list.py

@@ -61,7 +61,7 @@ item = Group(
 
 strings = Group(
     Items,
-    Statement(
+    Sequence(
         Keyword("strings", True),
         OpenBracket(),
         Delimited(

gtkblueprinttool/extensions/gtk_styles.py

@@ -46,7 +46,7 @@ class StyleClass(AstNode):
 
 styles = Group(
     Styles,
-    Statement(
+    Sequence(
         Keyword("styles", True),
         OpenBracket(),
         Delimited(