Specs: strip @nonnull annotations since they're too verbose

sky/specs/pointer.md

Index: sky/specs/pointer.md
diff --git a/sky/specs/pointer.md b/sky/specs/pointer.md
index 77adcff6c2664538bb71f701a504612a6bdec8c7..eaf17f27de6515b430c09cda45443779e245f07f 100644
--- a/sky/specs/pointer.md
+++ b/sky/specs/pointer.md
@@ -366,10 +366,10 @@ abstract class PointerEvent<T> extends Event<T> {
   final PointerKind kind;
   final double x; // logical pixels
   final double y; // logical pixels
-  final @nonnull double dx; // logical pixels
-  final @nonnull double dy; // logical pixels
+  final double dx; // logical pixels
+  final double dy; // logical pixels
 
-  final @nonnull int buttons; // bit field
+  final int buttons; // bit field
   static const int primaryMouseButton = 0x01;
   static const int secondaryMouseButton = 0x02;
   static const int primaryStylusButton = 0x02;
@@ -378,9 +378,9 @@ abstract class PointerEvent<T> extends Event<T> {
   static const int backButton = 0x08;
   static const int forwardButton = 0x10;
 
-  final @nonnull bool down;
-  final @nonnull bool primary;
-  final @nonnull bool obscured;
+  final bool down;
+  final bool primary;
+  final bool obscured;
 
   // if down != true, these are all null
   final double pressure; // normalised, 0.0 means none, 1.0 means "normal"
@@ -479,7 +479,7 @@ class WheelEvent extends Event {
                }): super(bubbles: bubbles);
 
   final int wheel;
-  final @nonnull double delta; // revolutions (or fractions thereof)
+  final double delta; // revolutions (or fractions thereof)
   final int pointer;
   final double x; // logical pixels
   final double y; // logical pixels