Remove "sco" and "unixware" ports.

SCO OpenServer and SCO UnixWare are more or less dead platforms.
We have never had a buildfarm member testing the "sco" port, and
the last "unixware" member was last heard from in 2012, so it's
fair to doubt that the code even compiles anymore on either one.
Remove both ports.  We can always undo this if someone shows up
with an interest in maintaining and testing these platforms.

Discussion: <17177.1476136994@sss.pgh.pa.us>

src/template/sco

@@ -1 +0,0 @@
-CC="$CC -b elf"

src/template/unixware

@@ -1,41 +0,0 @@
-if test "$GCC" != yes; then
-  # The -Kno_host is for a bug in the compiler.  See -hackers
-  # discussion on 7-8/Aug/2003.
-  cat >conftest.c <<__EOF__
-extern char *strcpy(char *, const char *);
-
-static void f(char *p, int n){
-        strcpy(p+n,"");
-}
-void g(void){
-        f(0, 0);
-}
-__EOF__
-
-  # Debugging and optimization are mutually exclusive
-  if test "$enable_debug" != yes; then
-    CFLAGS="-O"
-  fi
-  if $CC -c -O -Kinline conftest.c >conftest.err 2>&1; then
-    CFLAGS="$CFLAGS -Kinline"
-  else
-    CFLAGS="$CFLAGS -Kinline,no_host"
-  fi
-  rm -f conftest.*
-
-  PTHREAD_CFLAGS="-Kpthread"
-
-# The effect of doing threading for the backend does not work
-# because of a threading bug that appears in the regression tests:
-#
-# in make check, the plpgsql test (plpgsql.sql)
-# set statement_timeout to 1000;
-# select blockme();
-# reset statement_timeout;
-#
-# per report from Olivier PRENANT <ohp@pyrenet.fr>
-
-fi
-
-# Unixware's ldap library reportedly needs these too
-EXTRA_LDAP_LIBS="-llber -lresolv"