Remove dependency management for ANTLR 2

Closes gh-32149

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -14,16 +14,6 @@ bom {
 			issueLabels = ["type: dependency-upgrade"]
 		}
 	}
-	library("ANTLR2", "2.7.7") {
-		prohibit("20030911") {
-			because "it is old version that used a different versioning scheme"
-		}
-		group("antlr") {
-			modules = [
-				"antlr"
-			]
-		}
-	}
 	library("Artemis", "2.23.1") {
 		group("org.apache.activemq") {
 			modules = [