[Micronaut] remove duplicate JsonTypeName

[pbthorste]

In some cases, where the openapi file uses a discriminator, @JsonTypeName will appear twice - causing an error. This PR removes it from typeInfoAnnotation.mustache since it will always be included in pojo.mustache

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[wing328]

@pbthorste thanks for the PR. I'm able to repeat the issue and confirmed the fix:

@@ -49,7 +49,6 @@ import javax.annotation.Generated;
   @JsonSubTypes.Type(value = Whale.class, name = "whale"),
   @JsonSubTypes.Type(value = Zebra.class, name = "zebra"),
 })
-@JsonTypeName("mammal")

as @JsonTypeName("mammal") already present already in the code.

[wing328]

cc @andriy-dmytruk