Remove toolchains from maven pom-xml, since Java 7 is now being used

The corresponding documentation was already removed in
https://github.com/h2database/h2database/commit/197daa58104de6185e08b66e836876eb46b39844

h2/pom.xml

@@ -219,26 +219,6 @@
           </execution>
         </executions>
       </plugin>
-      <!-- Maven requires at least JRE 1.7 but we want to build with JDK 1.6 -->
-      <plugin>
-        <groupId>org.apache.maven.plugins</groupId>
-        <artifactId>maven-toolchains-plugin</artifactId>
-        <version>1.1</version>
-        <executions>
-          <execution>
-            <goals>
-              <goal>toolchain</goal>
-            </goals>
-          </execution>
-        </executions>
-        <configuration>
-          <toolchains>
-            <jdk>
-              <version>1.6</version>
-            </jdk>
-          </toolchains>
-        </configuration>
-      </plugin>
       <!-- Make sure we are not using anything outside JDK 1.6 -->
       <plugin>
         <groupId>org.codehaus.mojo</groupId>