If you use something like notepad++, use regex search/replace.
search: \.\w*$
replace: <blank>
Tackles variable length and zero length extensions.
Translation:
\. <-- literal dot (as opposed to wildcard dot)
\w <-- any word character (a-z, A-Z, 0-9)
* <-- match last indefinitely, zero or more times.
$ <-- end of line anchor. This prevents the search from including filenames with dots. (i.e. my.text.file.txt)