remove `coqdoc` hack from Makefile patch

The standard variable `COQDOCEXTRAFLAGS` can achieve the same result,
in a less hackish way.

Makefile

@@ -59,9 +59,8 @@ mangle-namesCoqProject: commonCoqProject
 	  -print | scripts/module-toc-order.py >> $(COQ_PROJ)
 
 $(COQ_MAKEFILE): $(COQ_PROJ) scripts/Makefile.coq.patch
-	@coq_makefile -f $< -o $@
-	@# Patch HTML target to switch out color, and 
-	@# so that it parses comments and has links to ssreflect.
+	@coq_makefile -f $< -o $@ COQDOCEXTRAFLAGS = "--parse-comments --external https://math-comp.github.io/htmldoc/ mathcomp"
+	@# Patch HTML target to switch out color.
 	@# Also include Makefile.coqdocjs for 'htmlpretty' documentation target.
 	@patch -s < scripts/Makefile.coq.patch
 

scripts/Makefile.coq.patch

@@ -12,15 +12,6 @@
  # This file is generated by coq_makefile and contains many variable
  # definitions, like the list of .v files or the path to Coq
  include Makefile.conf
-@@ -211,7 +216,7 @@
- # these flags do NOT contain the libraries, to make them easier to overwrite
- COQFLAGS?=-q $(OTHERFLAGS) $(COQEXTRAFLAGS)
- COQCHKFLAGS?=-silent -o $(COQCHKEXTRAFLAGS)
--COQDOCFLAGS?=-interpolate -utf8 $(COQDOCEXTRAFLAGS)
-+COQDOCFLAGS?=-interpolate -utf8 --parse-comments --external https://math-comp.github.io/htmldoc/ mathcomp $(COQDOCEXTRAFLAGS)
- 
- COQDOCLIBS?=$(COQLIBS_NOML)
- 
 @@ -480,6 +485,9 @@
  	$(HIDE)mkdir -p html
  	$(HIDE)$(COQDOC) \