Remove unsupported ja_JP translations

locale/ja_JP.po

@@ -1,19 +0,0 @@
-#
-msgid ""
-msgstr "Content-Type: text/plain; charset=utf-8\n"
-
-msgctxt "field:production.routing.operation,timesheet_available:"
-msgid "Available on timesheets"
-msgstr ""
-
-msgctxt "field:production.work,timesheet_available:"
-msgid "Available on timesheets"
-msgstr ""
-
-msgctxt "field:production.work,timesheet_lines:"
-msgid "Timesheet Lines"
-msgstr ""
-
-msgctxt "field:production.work,timesheet_works:"
-msgid "Timesheet Works"
-msgstr ""