Revert "Create empty translation files for Japanese"

This reverts commit bcdb31a.

Author: tkoyama010

locales/ja/LC_MESSAGES/CONTRIBUTING.po

@@ -43,7 +43,7 @@
 ## Localization options (translations)
 
 # List of languages for which locales will be generated in (/locales/<lang>)
-LANGUAGES = ["es", "ja"]
+LANGUAGES = ["es"]
 
 # List of languages that should be built when releasing the guide (docs or docs-test sessions)
 RELEASE_LANGUAGES = []