Merge pull request moby#5527 from dvdksn/docs-remove-dup-section

docs: remove duplicate parser directives bullet list

Author: crazy-max

frontend/dockerfile/docs/reference.md

@@ -192,11 +192,6 @@ following lines are all treated identically:
 #	  dIrEcTiVe=value
 ```
 
-The following parser directives are supported:
-
-- `syntax`
-- `escape`
-
 ### syntax
 
 <a name="external-implementation-features"><!-- included for deep-links to old section --></a>