runtime/doc: remove doctags

nvim is a dependency of the main tags task, and it's very unlikely that
one would need to build tags without having nvim available.

.gitignore

@@ -62,7 +62,6 @@ local.mk
 # runtime/doc
 /runtime/doc/*.html
 /runtime/doc/tags.ref
-/runtime/doc/doctags
 /runtime/doc/errors.log
 
 # clint errors, generated by `make lint`

runtime/doc/doctags.c

@@ -1,83 +0,0 @@
-/* vim:set ts=4 sw=4:
- * this program makes a tags file for vim_ref.txt
- *
- * Usage: doctags vim_ref.txt vim_win.txt ... >tags
- *
- * A tag in this context is an identifier between stars, e.g. *c_files*
- */
-
-#include <stdio.h>
-#include <string.h>
-#include <ctype.h>
-#include <stdlib.h>
-
-#define LINELEN 200
-
-	int
-main(argc, argv)
-	int		argc;
-	char	**argv;
-{
-	char	line[LINELEN];
-	char	*p1, *p2;
-	char	*p;
-	FILE	*fd;
-
-	if (argc <= 1)
-	{
-		fprintf(stderr, "Usage: doctags docfile ... >tags\n");
-		exit(1);
-	}
-	printf("help-tags\ttags\t1\n");
-	while (--argc > 0)
-	{
-		++argv;
-		fd = fopen(argv[0], "r");
-		if (fd == NULL)
-		{
-			fprintf(stderr, "Unable to open %s for reading\n", argv[0]);
-			continue;
-		}
-		while (fgets(line, LINELEN, fd) != NULL)
-		{
-			p1 = strchr(line, '*');				/* find first '*' */
-			while (p1 != NULL)
-			{
-				p2 = strchr(p1 + 1, '*');		/* find second '*' */
-				if (p2 != NULL && p2 > p1 + 1)	/* skip "*" and "**" */
-				{
-					for (p = p1 + 1; p < p2; ++p)
-						if (*p == ' ' || *p == '\t' || *p == '|')
-							break;
-					/*
-					 * Only accept a *tag* when it consists of valid
-					 * characters, there is white space before it and is
-					 * followed by a white character or end-of-line.
-					 */
-					if (p == p2
-							&& (p1 == line || p1[-1] == ' ' || p1[-1] == '\t')
-								&& (strchr(" \t\n\r", p[1]) != NULL
-									|| p[1] == '\0'))
-					{
-						*p2 = '\0';
-						++p1;
-						printf("%s\t%s\t/*", p1, argv[0]);
-						while (*p1)
-						{
-							/* insert backslash before '\\' and '/' */
-							if (*p1 == '\\' || *p1 == '/')
-								putchar('\\');
-							putchar(*p1);
-							++p1;
-						}
-						printf("*\n");
-						p2 = strchr(p2 + 1, '*');		/* find next '*' */
-					}
-				}
-				p1 = p2;
-			}
-		}
-		fclose(fd);
-	}
-	return 0;
-}