for i in *._.*; do echo mv "$i" "$(echo $i | sed 's/_.//g')"; done
Run this code to get a preview of what mv will do to your files. I created 3 files with the ._.name.txt to test the code. I ran the code above to test the results and here is the output.
mv file1._.name.txt file1.name.txt
mv file2._.name.txt file2.name.txt
mv file3._.name.txt file3.name.txt
As you can see it does what you want. Nothing has been alter to the files because the first echo command only prints command syntax. It shows you a preview of what it will do to the files.
To really make the changes to your files remove the first echo command after do. The code will now be:
for i in *._.*; do mv "$i" "$(echo $i | sed 's/_.//g')"; done
PS: Whenever you do a bulk rename to your files it is always a good idea to precede the command syntax with echo to get a preview. Then remove it if satisfy with the preview output.