chore: don't overly type map serialization

Author: JordonPhillips

codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/JsonShapeSerVisitor.java

@@ -94,10 +94,8 @@ public void serializeMap(GenerationContext context, MapShape shape) {
 
         // Get the right serialization for each entry in the map. Undefined
         // inputs won't have this serializer invoked.
-        writer.openBlock("return Object.entries(input).reduce((acc: $T, [key, value]: [$T, any]) => {",
-            "}, {});",
-            symbolProvider.toSymbol(shape),
-            symbolProvider.toSymbol(shape.getKey()),
+        writer.openBlock("return Object.entries(input).reduce((acc: {[key: string]: any}, "
+                + "[key, value]: [$1T, any]) => {", "}, {});", symbolProvider.toSymbol(shape.getKey()),
             () -> {
                 writer.openBlock("if (value === null) {", "}", () -> {
                     // Handle the sparse trait by short circuiting null values