* symbian/*: removed Symbian support.
  [Feature #10199][ruby-core:64725]
* dln.c: ditto.
* include/ruby/defines.h: ditto.
* thread_pthread.c: ditto.
* vm.c: ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47383 b2dd03c8-39d4-4d8f-98ff-823fe69b080e