Remove deprecated method (plus JSpecify alignment)

See gh-35594

spring-core/src/main/java/org/springframework/util/PlaceholderParser.java

@@ -314,14 +314,14 @@ final class PlaceholderParser {
 
 		private final boolean ignoreUnresolvablePlaceholders;
 
-		private final Function<String, List<Part>> parser;
+		private final Function<String, @Nullable List<Part>> parser;
 
 		private final PlaceholderResolver resolver;
 
 		private @Nullable Set<String> visitedPlaceholders;
 
 		PartResolutionContext(PlaceholderResolver resolver, String prefix, String suffix,
-				boolean ignoreUnresolvablePlaceholders, Function<String, List<Part>> parser) {
+				boolean ignoreUnresolvablePlaceholders, Function<String, @Nullable List<Part>> parser) {
 			this.prefix = prefix;
 			this.suffix = suffix;
 			this.ignoreUnresolvablePlaceholders = ignoreUnresolvablePlaceholders;

spring-core/src/main/java/org/springframework/util/PropertyPlaceholderHelper.java

@@ -96,11 +96,6 @@ public class PropertyPlaceholderHelper {
 		return this.parser.replacePlaceholders(value, placeholderResolver);
 	}
 
-	@Deprecated(since = "6.2.12", forRemoval = true)
-	protected String parseStringValue(String value, PlaceholderResolver placeholderResolver) {
-		return this.parser.replacePlaceholders(value, placeholderResolver);
-	}
-
 
 	/**
 	 * Strategy interface used to resolve replacement values for placeholders contained in Strings.