Remove dead ports

Remove the following ports:

- dgux
- nextstep
- sunos4
- svr4
- ultrix4
- univel

These are obsolete and not worth rescuing.  In most cases, there is
circumstantial evidence that they wouldn't work anymore anyway.

src/template/dgux

@@ -1 +0,0 @@
-# src/template/dgux

src/template/nextstep

@@ -1,5 +0,0 @@
-# src/template/nextstep
-
-AROPT=rc
-SHARED_LIB=
-DLSUFFIX=.o

src/template/sunos4

@@ -1,7 +0,0 @@
-if test "$GCC" != yes ; then
-  CC="$CC -Xa"			# relaxed ISO C mode
-  CFLAGS="-v -DSUNOS_CC"	# -v is like gcc -Wall
-  if test "$enable_debug" != yes; then
-    CFLAGS="$CFLAGS -O"		# any optimization breaks debug
-  fi
-fi

src/template/univel

@@ -1,2 +0,0 @@
-CFLAGS="-v -O -K i486,host,inline,loop_unroll -Dsvr4"
-LIBS="-lc89"