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/makefiles/Makefile.dgux

@@ -1,9 +0,0 @@
-AROPT = crs
-DLSUFFIX = .so
-CFLAGS_SL = -fpic
-
-# Rule for building a shared library from a single .o file
-%.so: %.o
-	$(CC) $(CFLAGS) $(LDFLAGS) $(LDFLAGS_SL) -shared -o $@ $<
-
-sqlmansect = 5

src/makefiles/Makefile.sunos4

@@ -1,12 +0,0 @@
-AROPT = cr
-
-DLSUFFIX = .so
-ifeq ($(GCC), yes)
-CFLAGS_SL = -fpic
-else
-CFLAGS_SL = -PIC
-endif
-
-# Rule for building a shared library from a single .o file
-%.so: %.o
-	$(LD) -assert pure-text -Bdynamic -o $@ $<

src/makefiles/Makefile.svr4

@@ -1,15 +0,0 @@
-# MAKE_EXPORTS is required for svr4 loaders that want a file of
-# symbol names to tell them what to export/import.
-#MAKE_EXPORTS= true
-
-LIBS += -lc /usr/ucblib/libucb.a
-LDFLAGS += -LD-Blargedynsym
-
-DLSUFFIX = .so
-CFLAGS_SL =
-
-# Rule for building a shared library from a single .o file
-%.so: %.o
-	$(LD) -G -Bdynamic -o $@ $<
-
-sqlmansect = 5

src/makefiles/Makefile.ultrix4

@@ -1,11 +0,0 @@
-# used by initdb
-SHELL=/bin/sh5
-AROPT = crs
-
-DLSUFFIX = .so
-# "-G 0" works for both DEC cc and GNU cc.
-CFLAGS_SL = -G 0
-
-# Rule for building a shared library from a single .c file
-%.so: %.c
-	$(CC) -c -G 0 $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $(LDFLAGS_SL) -o $@ $<

src/makefiles/Makefile.univel

@@ -1,10 +0,0 @@
-AROPT = crs
-export_dynamic = -Wl,-Bexport
-DLSUFFIX = .so
-CFLAGS_SL = -K PIC
-
-# Rule for building a shared library from a single .o file
-%.so: %.o
-	$(LD) -G -Bdynamic -o $@ $<
-
-sqlmansect = 5