Remove unnecessary escapes in regular expressions

See gh-24470

spring-aop/src/main/java/org/springframework/aop/interceptor/CustomizableTraceInterceptor.java

@@ -147,7 +147,7 @@ public class CustomizableTraceInterceptor extends AbstractTraceInterceptor {
 	/**
 	 * The {@code Pattern} used to match placeholders.
 	 */
-	private static final Pattern PATTERN = Pattern.compile("\\$\\[\\p{Alpha}+\\]");
+	private static final Pattern PATTERN = Pattern.compile("\\$\\[\\p{Alpha}+]");
 
 	/**
 	 * The {@code Set} of allowed placeholders.