Drop 1.16.5 support to use Mojang mappings

Because there is no option to create a `remapped-mojang` artifact for 1.16.5 and the whole point of the scripts is to save me time, 1.16.5 support is being removed earlier than usual.

Also fixes issues with NMS-based shulker collision check.
Closes #36

pom.xml

@@ -37,7 +37,6 @@
       <modules>
         <module>api</module>
         <module>plugin</module>
-        <module>internal/v1_16_R3</module>
         <module>internal/v1_17_R1</module>
         <module>assembly</module>
       </modules>
@@ -139,6 +138,12 @@
           <groupId>org.apache.maven.plugins</groupId>
           <version>3.3.0</version>
         </plugin>
+
+        <plugin>
+          <groupId>net.md-5</groupId>
+          <artifactId>specialsource-maven-plugin</artifactId>
+          <version>1.2.2</version>
+        </plugin>
       </plugins>
     </pluginManagement>
   </build>