You could code a database patch in PHP/with the WordPress APIs, but since it sounds like you won’t be repeating this process frequently, I think that’s probably overkill. The most straightforward approach to bulk changes like this is a quick SQL update directly on the database.
Bulk Update via SQL Query
One large exception to performing a bulk update with a direct SQL query is the case where the fields you intend to modify contain serialized data, in which case using PHP/the WordPress APIs or a specialized tool might prove more convenient.
Luckily, post slugs are stored as plain strings in the post_name field, so a query to remove trailing hyphens is fairly intuitive:
UPDATE wp_posts SET post_name = TRIM(TRAILING "-" FROM post_name) WHERE post_name LIKE "%-"
Since direct SQL queries circumvent all manner of checks and balances, it is prudent to back up your database before executing any database-altering query.
Link Redirection via Server Configuration
Since it sounds like this content has been around for while and you might have users attempting to access it using old, hyphen-terminated URLs, you may want to add a rewrite rule to your .htaccess file (or equivalent) in order to redirect old URLs to their new hyphen-less counterparts:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)-$ $1 [QSA,R=301,L] # Redirect requests to hyphen-terminated URLs
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
This may need to be modified to fit your installation’s configuration. Note that it will interfere with any other functionality that depends on non-filesystem, hyphen-terminated URLs, if it exists.