Remove Netty dependency management that's now part of its bom

The native-epoll and native-kqueue modules are now managed by
Netty's bom. We need to retain the dependency management for
native-unix-common for the time being due to a bug [1] in Netty's
bom.

[1] netty/netty#6849

Closes gh-9471

spring-boot-dependencies/pom.xml

@@ -836,16 +836,6 @@
 				<scope>import</scope>
 				<type>pom</type>
 			</dependency>
-			<dependency>
-				<groupId>io.netty</groupId>
-				<artifactId>netty-transport-native-epoll</artifactId>
-				<version>${netty.version}</version>
-			</dependency>
-			<dependency>
-				<groupId>io.netty</groupId>
-				<artifactId>netty-transport-native-kqueue</artifactId>
-				<version>${netty.version}</version>
-			</dependency>
 			<dependency>
 				<groupId>io.netty</groupId>
 				<artifactId>netty-transport-native-unix-common</artifactId>