test command-line: remove unnecessary encoding logic

GitHub: ref groongaGH-2172

Issue

When running grndb tests in a Windows environment, encoding file paths
containing Japanese characters failed in the test logs. It caused tests to
fail.

Cause

This issue occurred because log file encoded in UTF-8 were
misinterpreted as CP932 and then converted to UTF-8.

Soulution

Groonga logs are originally in UTF-8 so we don't have to convert.
We just remove the encodeing logic from test's helper.

test/command_line/helper/groonga_log.rb

@@ -232,7 +232,7 @@ def groonga_log_content
   end
 
   def normalized_groonga_log_content
-    normalize_groonga_log(groonga_log_content).encode("locale")
+    normalize_groonga_log(groonga_log_content)
   end
 
   private