Cleanup and maintenance

Updates Spigot version
Removes MockBukkit and related tests, as it makes updating a hassle
Bumps API version to 1.20
Removes legacy sign updating

pom.xml

@@ -4,7 +4,7 @@
 
     <groupId>net.knarcraft</groupId>
     <artifactId>Stargate</artifactId>
-    <version>0.11.5.10</version>
+    <version>0.11.5.11</version>
 
     <licenses>
         <license>
@@ -53,7 +53,7 @@
         <dependency>
             <groupId>org.spigotmc</groupId>
             <artifactId>spigot-api</artifactId>
-            <version>1.20-R0.1-SNAPSHOT</version>
+            <version>1.21.8-R0.1-SNAPSHOT</version>
             <scope>provided</scope>
         </dependency>
         <dependency>
@@ -62,12 +62,6 @@
             <version>1.7.1</version>
             <scope>provided</scope>
         </dependency>
-        <dependency>
-            <groupId>com.github.seeseemelk</groupId>
-            <artifactId>MockBukkit-v1.18</artifactId>
-            <version>2.85.2</version>
-            <scope>test</scope>
-        </dependency>
         <dependency>
             <groupId>org.jetbrains</groupId>
             <artifactId>annotations</artifactId>