Don't list the same annotation twice

This was introduced via search-and-replace in d8216e8.

Fixes #1340

COPYBARA_INTEGRATE_REVIEW=#1340 from mernst:remove-duplicate-type-annotation 2bb3000
PiperOrigin-RevId: 874817120

Author: mernst

core/src/main/java/com/google/googlejavaformat/java/JavaInputAstVisitor.java

@@ -301,7 +301,6 @@ private static ImmutableSetMultimap<String, String> typeAnnotations() {
         ImmutableList.of(
             "org.jspecify.annotations.NonNull",
             "org.jspecify.annotations.Nullable",
-            "org.jspecify.annotations.Nullable",
             "org.checkerframework.checker.nullness.qual.NonNull",
             "org.checkerframework.checker.nullness.qual.Nullable")) {
       String simpleName = annotation.substring(annotation.lastIndexOf('.') + 1);