Remove unnecessary assert statement, Fix regex_replace docstring and simplify regex_replace

docs/customize/Tokenizers.md

@@ -67,8 +67,9 @@ Here is an example configuration file:
 
 ``` yaml
 query-preprocessing:
+    - step: split_japanese_phrases
     - step: regex_replace
-    replacements:
+      replacements:
         - pattern: https?://[^\s]* # Filter URLs starting with http or https
           replace: ''
     - step: normalize
@@ -111,6 +112,8 @@ The following is a list of preprocessors that are shipped with Nominatim.
         heading_level: 6
         docstring_section_style: spacy
 
+##### regex-replace
+
 ::: nominatim_api.query_preprocessing.regex_replace
     options:
         members: False