Remove extraneous declare in .d.ts output to better match strada

[Copilot]

The declare modifier is completely redundant in declaration files since everything is ambient by definition. This removes it from all .d.ts output, aligning with strada's behavior.

Changes

• ensureModifierFlags: Added ModifierFlagsAmbient to the exclusion mask so it's always stripped, removed the needsDeclare-based addition logic
• Synthetic declarations: Removed 4 inline if tx.needsDeclare blocks that conditionally added KindDeclareKeyword to generated variable statements
• transformExpandoHost: Removed modifierFlags |= ast.ModifierFlagsAmbient for default export expando hosts

Before/After

-export declare const obj: { ... };
-declare function foo(): void;
+export const obj: { ... };
+function foo(): void;

Baseline impact

443 .diff baseline files deleted (output now matches strada reference).