Remove unnecessary alias references [ci-skip]

RDoc lists method aliases automatically.

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -983,7 +983,6 @@ def index_name_exists?(table_name, index_name)
       # Adds a reference. The reference column is a bigint by default,
       # the <tt>:type</tt> option can be used to specify a different type.
       # Optionally adds a +_type+ column, if <tt>:polymorphic</tt> option is provided.
-      # #add_reference and #add_belongs_to are acceptable.
       #
       # The +options+ hash can include the following keys:
       # [<tt>:type</tt>]
@@ -1034,7 +1033,6 @@ def add_reference(table_name, ref_name, **options)
       alias :add_belongs_to :add_reference
 
       # Removes the reference(s). Also removes a +type+ column if one exists.
-      # #remove_reference and #remove_belongs_to are acceptable.
       #
       # ====== Remove the reference
       #