Strip out references to 'relaxed-emphasis' configuration option.

Relaxed-emphasis is now always built, then controlled with a runtime off switch. This commit manually follows upstream commit b787bc3459 to synchronize (about relax) with the discount source root one directory up.

Plan9/README

@@ -17,7 +17,6 @@
 		--enable-pandoc-header	Use pandoc-style header blocks
 		--enable-superscript	A^B becomes A<sup>B</sup>
 		--enable-amalloc	Enable memory allocation debugging
-		--relaxed-emphasis	underscores aren't special in the middle of words
 		--with-tabstops=N	Set tabstops to N characters (default is 4)
 		--enable-div		Enable >%id% divisions
 		--enable-alpha-list	Enable (a)/(b)/(c) lists

Plan9/markdown.2

@@ -122,7 +122,7 @@ tags from the output.
 Suppress Smartypants-style replacement of quotes, dashes, or ellipses.
 .TP
 .B MKD_STRICT
-Disable superscript and relaxed emphasis processing if configured; otherwise a no-op.
+Disable superscript and relaxed emphasis processing.
 .TP
 .B MKD_TAGTEXT
 Process as inside an

Plan9/markdown.6

@@ -520,9 +520,7 @@ cell in the column.
 A colon at both ends of a column's header dashes indicates center alignment.
 .TP
 Relaxed Emphasis
-If configured with
-.BR --relaxed-emphasis ,
-the rules for emphasis are changed so that a single
+The rules for emphasis are changed so that a single
 .B _
 will not count as an emphasis character in the middle of a word.
 This is useful for documenting some code where