Cleanup: remove BLENDER_USER_AUTOSAVE

This was only used on WIN32 when the temporary directory didn't exist.
When the check was added [0] this made some sense because it relied on
`U.tempdir` existing, since then additional checks have been added to
ensure a temporary directory can be used. Further, this fall-back
location isn't documented in the user manual.

[0]: 615db01b01

scripts/modules/bpy/utils/__init__.py

@@ -739,7 +739,7 @@ def user_resource(resource_type, *, path="", create=False):
     """
     Return a user resource path (normally from the users home directory).
 
-    :arg type: Resource type in ['DATAFILES', 'CONFIG', 'SCRIPTS', 'AUTOSAVE'].
+    :arg type: Resource type in ['DATAFILES', 'CONFIG', 'SCRIPTS'].
     :type type: string
     :arg path: Optional subdirectory.
     :type path: string

scripts/modules/sys_info.py

@@ -96,7 +96,6 @@ def write_sysinfo(filepath):
             output.write("datafiles: %r\n" % (bpy.utils.user_resource('DATAFILES')))
             output.write("config: %r\n" % (bpy.utils.user_resource('CONFIG')))
             output.write("scripts: %r\n" % (bpy.utils.user_resource('SCRIPTS')))
-            output.write("autosave: %r\n" % (bpy.utils.user_resource('AUTOSAVE')))
             output.write("tempdir: %r\n" % (bpy.app.tempdir))
 
             output.write(title("FFmpeg"))