docs: Formatted spacing and updated documentation (#3290)

* Refactored redundant spacing in pom.xml

* Updated documentation of remove subscriber in publish-subscribe model

pom.xml

@@ -231,7 +231,7 @@
     <module>table-module</module>
     <module>template-method</module>
     <module>templateview</module>
-      <module>thread-pool-executor</module>
+    <module>thread-pool-executor</module>
     <module>throttling</module>
     <module>tolerant-reader</module>
     <module>trampoline</module>
@@ -244,8 +244,8 @@
     <module>version-number</module>
     <module>virtual-proxy</module>
     <module>visitor</module>
-      <module>backpressure</module>
+    <module>backpressure</module>
-      <module>actor-model</module>
+    <module>actor-model</module>
 
   </modules>
   <repositories>

publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/model/Topic.java

@@ -51,7 +51,7 @@ public class Topic {
   }
 
   /**
-   * Remove a subscriber to the list of subscribers.
+   * Remove a subscriber from the list of subscribers.
    *
    * @param subscriber subscriber to remove
    */