Don't quote executable name twice in script headers

Don't quote the executable name in JythonCommandSpec.from_environment() since it is quoted if necessary in CommandSpec._render().

With the executable quoted on initialisation of JythonCommandSpec, the quotes get escaped in the resulting header, eg:

#!/usr/bin/env \"/path/to/jython\"

setuptools/command/easy_install.py

@@ -1944,15 +1944,6 @@ class JythonCommandSpec(CommandSpec):
             __import__('java').lang.System.getProperty('os.name') != 'Linux'
         )
 
-    @classmethod
-    def from_environment(cls):
-        string = '"' + cls._sys_executable() + '"'
-        return cls.from_string(string)
-
-    @classmethod
-    def from_string(cls, string):
-        return cls([string])
-
     def as_header(self):
         """
         Workaround Jython's sys.executable being a .sh (an invalid