Remove the bin_size return

When we return a bin_size (such as 28672), the web client does not
accept it as as bin size and try to use it as value for the b64 src of
the image.  Though, returning the image as b64 in all cases does seem to
be supported.

attachment_s3/models/ir_attachment.py

@@ -43,7 +43,7 @@ class IrAttachment(models.Model):
 
     @api.depends('store_fname', 'db_datas')
     def _compute_datas(self):
-        bin_size = self._context.get('bin_size')
+        bin_size = self.env.context.get('bin_size')
         if self._s3_readonly():
             for attach in self:
                 # look first in db_datas in case a file has been modified
@@ -165,10 +165,7 @@ class IrAttachment(models.Model):
     def _file_read_s3(self, bucket, fname, bin_size=False):
         filekey = bucket.get_key(fname)
         if filekey:
-            if bin_size:
-                read = filekey.size
-            else:
-                read = base64.b64encode(filekey.get_contents_as_string())
+            read = base64.b64encode(filekey.get_contents_as_string())
         else:
             # If the attachment has been created before the installation
             # of the addon, it might be stored on the filesystem.