As far as I understand.. you want to remove the "Delete" action in Thunar.
Keep in mind that those are "Default Actions" not "Custom Actions". They are in the Thunar's source code.
In order to remove the "Delete" default action you should download the source code, edit, and then recompile it.
NOTE: In my case I'm running Xubuntu 13.04 with Thunar 1.6.2
You can try the following:
1) Open a Terminal and install the necessary packages.
sudo apt-get install build-essential
2) Install build dependencies
sudo apt-get build-dep thunar
3) Create a folder to download the source code.
mkdir ~/Downloads/src
cd ~/Downloads/src
4) Download the source code.
5) Edit the the file "thunar-standard-view.c"
mousepad thunar-1.6.2/thunar/thunar-standard-view.c
You should remove the line number "402" and save the changes.
{ "delete", GTK_STOCK_DELETE, N_ ("_Delete"), NULL, NULL, G_CALLBACK
(thunar_standard_view_action_delete), },
Before:
After:
6) Go to the "thunar-1.6.2" folder to build the deb packages.
cd thunar-1.6.2/
dpkg-buildpackage -rfakeroot -uc -b
7) Now you can install the deb packages.
8) Finally you can logout and Login to see the changes.
9) Your thunar file manager should look like this:
(without the "Delete" Action")
hope it helps.