Testlib/generate_expected_output.py: Fix encoding.

Do not apply additional encoding when reading process output.
Fixes errors when encountering UTF-8:

Traceback (most recent call last):
  File "./generate_expected_output.py", line 117, in <module>
    generateTestData(path)
  File "./generate_expected_output.py", line 106, in generateTestData
    out.write(data.decode('utf-8'))
UnicodeEncodeError: 'ascii' codec can't encode character u'\xdc' in position 5485: ordinal not in range(128)

Change-Id: Ib827787a59a18b4d3d0601645856517f43c01fc3
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>

tests/auto/testlib/selftests/generate_expected_output.py

@@ -105,7 +105,7 @@ def generateTestData(testname):
         result = 'expected_' + testname + '.' + format
         data = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True).communicate()[0]
         out = open(result, 'w')
-        out.write(data.decode('utf-8'))
+        out.write(data)
         out.close()
         replaceInFile(result)