Remove deprecated configuration properties

This commit removes the following deprecated properties:

* `server.connection-timeout`
* `server.use-forward-headers`
* `server.jetty.max-http-post-size`
* `server.tomcat.max-http-post-size`

Closes gh-20991

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-tomcat/src/main/resources/application.properties

@@ -1,3 +1,3 @@
 server.compression.enabled: true
 server.compression.min-response-size: 1
-server.connection-timeout=5000
+server.tomcat.connection-timeout=5s