patch 8.1.1730: wrong place for mark viminfo support

Problem:    Wrong place for mark viminfo support.
Solution:   Move it to viminfo.c. (Yegappan Lakshmanan, closes #4716)

src/structs.h

@@ -123,6 +123,7 @@ typedef struct {
 // alphabet coding.  To minimize changes to the code, I decided to just
 // increase the number of possible marks.
 #define NMARKS		('z' - 'a' + 1)	// max. # of named marks
+#define EXTRA_MARKS	10		// marks 0-9
 #define JUMPLISTSIZE	100		// max. # of marks in jump list
 #define TAGSTACKSIZE	20		// max. # of tags in tag stack