[python] Remove double quotes from unicode values

When converting a ledger.Value to unicode the Python API added
double quotes around it.

src/py_value.cc

@@ -325,7 +325,6 @@ void export_value()
     .def("to_mask", &value_t::to_mask)
     .def("to_sequence", &value_t::to_sequence)
 
-    .def("__unicode__", py_dump_relaxed)
     .def("__repr__", py_dump)
 
     .def("casted", &value_t::casted)

test/regress/B21BF389.py

@@ -0,0 +1,9 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+from __future__ import print_function, unicode_literals
+
+import ledger
+
+for post in ledger.read_journal(__file__.replace(".py", "_py.test")).query("income"):
+  print(unicode(post.tag("Reference")))

test/regress/B21BF389_py.test

@@ -0,0 +1,8 @@
+2016/01/11 * Employer
+  Assets:Checking
+  Income:Salary                 € 1.500,00
+    ; Reference: Christmas bonus
+
+test python test/regress/B21BF389.py
+Christmas bonus
+end test