Set the version by properties value in dependency management. (#2362)

Remove the version setting in dependencies.
Remove the scala compiler version property.

pom.xml

@@ -17,7 +17,8 @@
   ~
   -->
 
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
 
     <groupId>org.apache.skywalking</groupId>
@@ -82,7 +83,6 @@
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <compiler.version>1.8</compiler.version>
-        <scala.compiler.version>2.11.7</scala.compiler.version>
         <powermock.version>1.6.4</powermock.version>
         <checkstyle.version>6.18</checkstyle.version>
         <junit.version>4.12</junit.version>
@@ -114,13 +114,11 @@
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
-            <version>${junit.version}</version>
             <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-all</artifactId>
-            <version>${mockito-all.version}</version>
             <scope>test</scope>
         </dependency>
         <dependency>
@@ -140,13 +138,13 @@
             <dependency>
                 <groupId>junit</groupId>
                 <artifactId>junit</artifactId>
-                <version>4.12</version>
+                <version>${junit.version}</version>
                 <scope>test</scope>
             </dependency>
             <dependency>
                 <groupId>org.mockito</groupId>
                 <artifactId>mockito-all</artifactId>
-                <version>1.10.19</version>
+                <version>${mockito-all.version}</version>
                 <scope>test</scope>
             </dependency>
             <dependency>