Maven: remove unneeded properties

Those are determined automatically by gradle, no need to specify explicitly.

common.gradle

@@ -5,15 +5,15 @@
 apply plugin: 'java'
 apply plugin: 'maven'
 
-String mavenGroupId = 'com.jme3'
-String mavenVersion = jmeVersion + '-' + jmeVersionTag //'-SNAPSHOT'
+group   = 'com.jme3'
+version = jmeVersion + '-' + jmeVersionTag
 
 sourceCompatibility = '1.6'
 [compileJava, compileTestJava]*.options*.encoding = 'UTF-8'
 
 repositories {
     mavenCentral()
-    maven{
+    maven {
         url "http://nifty-gui.sourceforge.net/nifty-maven-repo"
     }
 }
@@ -23,11 +23,6 @@ dependencies {
     testCompile group: 'junit', name: 'junit', version: '4.10'
 }
 
-String mavenArtifactId = name
-
-group = mavenGroupId
-version = mavenVersion
-
 javadoc {
     failOnError = false
     options.memberLevel = org.gradle.external.javadoc.JavadocMemberLevel.PROTECTED
@@ -60,14 +55,6 @@ artifacts {
     }
 }
 
-configure(install.repositories.mavenInstaller) {
-    pom.project {
-        groupId = mavenGroupId
-        artifactId = mavenArtifactId
-        version = mavenVersion
-    }
-}
-
 task createFolders(description: 'Creates the source folders if they do not exist.') doLast {
 //    sourceSets*.allSource*.srcDirs*.each { File srcDir ->
 //        if (!srcDir.isDirectory()) {