refactoring: remove un-used code, add go doc, fix ci (#199)

Refactoring, consisting of
 - remove unused method `isAuxiliaryLanguage` and `FileCountList`
   in order to reduce public API surfaces (go/java)
 - add GoDoc to public APIs
 - ci: java profile use latest go src
  It also now mimics https://docs.travis-ci.com/user/languages/go/#go-import-path
  for non-go build image, as code relies on internal imports.

TEST PLAN:
 - make test

java/src/test/java/tech/sourced/enry/EnryTest.java

@@ -6,12 +6,6 @@ import static org.junit.Assert.*;
 
 public class EnryTest {
 
-    @Test
-    public void isAuxiliaryLanguage() {
-        assertTrue(Enry.isAuxiliaryLanguage("HTML"));
-        assertFalse(Enry.isAuxiliaryLanguage("Go"));
-    }
-
     @Test
     public void getLanguage() {
         String code = "<?php $foo = bar();";