How to rename files to exclude the datetime stamp?

You can use the rename command:

$ rename -n 's/ \(.*?\)//' *.png
icon-culture (2015_09_04 06_58_44 UTC).png renamed as icon-culture.png
icon-disk (2015_09_04 06_58_44 UTC).png renamed as icon-disk.png
icon-download (2015_09_04 06_58_44 UTC).png renamed as icon-download.png
icon-drop (2015_09_04 06_58_44 UTC).png renamed as icon-drop.png
icon-file (2015_09_04 06_58_44 UTC).png renamed as icon-file.png
icon-film (2015_09_04 06_58_44 UTC).png renamed as icon-film.png
icon-flag (2015_09_04 06_58_44 UTC).png renamed as icon-flag.png
icon-folder (2015_09_04 06_58_44 UTC).png renamed as icon-folder.png
icon-garbage (2015_09_04 06_58_44 UTC).png renamed as icon-garbage.png
icon-graph (2015_09_04 06_58_44 UTC).png renamed as icon-graph.png
icon-heart (2015_09_04 06_58_44 UTC).png renamed as icon-heart.png
icon-help (2015_09_04 06_58_44 UTC).png renamed as icon-help.png
icon-lock (2015_09_04 06_58_44 UTC).png renamed as icon-lock.png
icon-map (2015_09_04 06_58_44 UTC).png renamed as icon-map.png
icon-media (2015_09_04 06_58_44 UTC).png renamed as icon-media.png
icon-money (2015_09_04 06_58_44 UTC).png renamed as icon-money.png
icon-monitor (2015_09_04 06_58_44 UTC).png renamed as icon-monitor.png
icon-notes (2015_09_04 06_58_44 UTC).png renamed as icon-notes.png
icon-openmail (2015_09_04 06_58_44 UTC).png renamed as icon-openmail.png
icon-phone (2015_09_04 06_58_44 UTC).png renamed as icon-phone.png
icon-photo (2015_09_04 06_58_44 UTC).png renamed as icon-photo.png

s/ \(.*?\)// is a simple, if broad, expression, matching a space followed by parentheses-enclosed stuff. You can pick more precise expressions like:

• s/ \(.*?\)\.png$/.png/ - like the previous, but matching only if followed by .png and the end of the filename, or
• s/ \(\d{4}(_\d\d){2} \d\d(_\d\d){2} UTC\)\.png/.png/ - matching the date pattern shown in these files, and followed .png.

The -n option is for testing the command. Run without it if you're satisfied with the results.