Revert "pom.xml: specify minimum Maven version in prerequisites."

This reverts commit 6d4df11.

Fix warning from Maven:
[WARNING] The project ru.mystamps:mystamps:war:0.3-SNAPSHOT uses prerequisites which is only
intended for maven-plugin projects but not for non maven-plugin projects.

Fix #635

Author: php-coder

pom.xml

@@ -1039,8 +1039,4 @@
 		<url>https://github.com/php-coder/mystamps</url>
 	</scm>
 
-	<prerequisites>
-		<maven>3.2.1</maven>
-	</prerequisites>
-	
 </project>