symbian: drop support

The OS is deprecated. I see no traces of anyone having actually built
curl for Symbian after 2012.

The public headers are unmodified.

Closes curl#5989

Author: bagder

lib/Makefile.am

@@ -27,7 +27,7 @@ EXTRA_DIST = Makefile.m32 config-win32.h config-win32ce.h           \
  config-plan9.h config-riscos.h config-mac.h curl_config.h.in       \
  makefile.dj config-dos.h libcurl.plist libcurl.rc config-amigaos.h \
  makefile.amiga Makefile.netware nwlib.c nwos.c config-win32ce.h    \
- config-os400.h setup-os400.h config-symbian.h                      \
+ config-os400.h setup-os400.h                                       \
  config-tpf.h mk-ca-bundle.pl mk-ca-bundle.vbs $(CMAKE_DIST)        \
  firefox-db2pem.sh config-vxworks.h Makefile.vxworks checksrc.pl    \
  setup-win32.h

lib/asyn-ares.c

@@ -67,8 +67,8 @@
 #include "select.h"
 #include "progress.h"
 
-#  if defined(CURL_STATICLIB) && !defined(CARES_STATICLIB) && \
-     (defined(WIN32) || defined(__SYMBIAN32__))
+#  if defined(CURL_STATICLIB) && !defined(CARES_STATICLIB) &&   \
+  defined(WIN32)
 #    define CARES_STATICLIB
 #  endif
 #  include <ares.h>