rm obsolete /usr/5bin paths (Solaris patch 130-CR7019368)

This change is pulled from here:
https://github.com/oracle/solaris-userland/blob/master/components/ksh93/patches/130-CR7019368.patch

Author: McDutchie

src/cmd/INIT/regress.sh

@@ -1379,7 +1379,7 @@ esac
 export COLUMNS=80
 SOURCE=$PWD
 PATH=$SOURCE:${PATH#?(.):}
-PATH=${PATH%%:?(.)}:/usr/5bin:/bin:/usr/bin
+PATH=${PATH%%:?(.)}:/bin:/usr/bin
 UNIT=$1
 shift
 if	[[ -f $UNIT && ! -x $UNIT ]]

src/lib/libast/comp/mkdir.c

@@ -39,7 +39,7 @@ mkdir(const char* path, mode_t mode)
 	register int	n;
 	char*		av[3];
 
-	static char*	cmd[] = { "/bin/mkdir", "/usr/5bin/mkdir", 0 };
+	static char*	cmd[] = { "/bin/mkdir", 0 };
 
 
 	n = errno;

src/lib/libast/comp/rmdir.c

@@ -39,7 +39,7 @@ rmdir(const char* path)
 	struct stat	st;
 	char*		av[3];
 
-	static char*	cmd[] = { "/bin/rmdir", "/usr/5bin/rmdir", 0 };
+	static char*	cmd[] = { "/bin/rmdir", 0 };
 
 	if (stat(path, &st) < 0) return(-1);
 	if (!S_ISDIR(st.st_mode))

src/lib/libast/port/astconf.c

@@ -569,7 +569,7 @@ initialize(register Feature_t* fp, const char* path, const char* command, const
 						}
 						if (fp->op == OP_universe)
 						{
-							if (strneq(p, "xpg", 3) || strneq(p, "5bin", 4))
+							if (strneq(p, "xpg", 3))
 							{
 								ok = 1;
 								break;