This is a magical solution to a non-issue (aesthetic), it could easily be introduced by a plugin and is not a good substitute for proper web server configuration. Eg, Apache:
##
## Directory Listing attempts
##
DirectorySlash Off
RewriteOptions AllowNoSlash
##
## Redirect Trailing Slashes...
##
RewriteRule ^(.*)/$ /$1 [L,R=301]
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