Remove unused .1 => .txt rule (issue 557560044 by address@hidden)

[hanwenn]

Reviewers: ,

Message:
tested by running 'make dist'

Description:
Remove unused .1 => .txt rule

Please review this at https://codereview.appspot.com/557560044/

Affected files (+0, -5 lines):
  M stepmake/stepmake/documentation-rules.make


Index: stepmake/stepmake/documentation-rules.make
diff --git a/stepmake/stepmake/documentation-rules.make 
b/stepmake/stepmake/documentation-rules.make
index 
0f907ce822067343a79464e8eb94d41916ff9d9b..e6e87d25eb28d47671714f7e0a86ba0309e881e6
 100644
--- a/stepmake/stepmake/documentation-rules.make
+++ b/stepmake/stepmake/documentation-rules.make
@@ -10,8 +10,3 @@ $(outdir)/%.gif: %.xpm
 $(outdir)/%.png: %.xpm
        $(call ly_progress,Making,$@,< xpm)
        xpmtoppm $< | pnmtopng > $@
-
-# use striproff?
-$(outdir)/%.txt: $(outdir)/%.1
-       $(call ly_progress,Making,$@,< 1)
-       troff -man -Tascii $< | grotty -b -u -o > $@