Remove unnecessary extensions in t_filenm defaults

Remove unnecessary extensions in t_filenm defaults

Several tools had an extension specified for the default file name in
t_filenm, but that extension matched either the only accepted extension
for the file type, or to the default extension for that type.

To keep the code more uniform, remove those unnecessary declarations.
This leaves <10 instances where t_filenm specifies a non-default
extension for the default file name (which doesn't currently work).
Probably some of those could also be removed, but at least a few are
justified, so a subsequent commit will add support for that.

Change-Id: I28053b6b407783b515144aad5351f27bbc2b6ba7