Adds documentation of implicit regex match removal (#24934)

regex_replace has a implicit parameter for `replacement` and thus can remove the matched string

docs/docsite/rst/playbooks_filters.rst

@@ -588,6 +588,9 @@ To replace text in a string with regex, use the "regex_replace" filter::
 
     # convert "localhost:80" to "localhost, 80" using named groups
     {{ 'localhost:80' | regex_replace('^(?P<host>.+):(?P<port>\\d+)$', '\\g<host>, \\g<port>') }}
+    
+    # convert "localhost:80" to "localhost"
+    {{ 'localhost:80' | regex_replace(':80') }}
 
 .. note:: Prior to ansible 2.0, if "regex_replace" filter was used with variables inside YAML arguments (as opposed to simpler 'key=value' arguments),
    then you needed to escape backreferences (e.g. ``\\1``) with 4 backslashes (``\\\\``) instead of 2 (``\\``).