Revert async process substitution & completion strategy

They're not quite ready. Keep them on a feature branch for now.

spec/options/async_zpty_name_spec.rb

@@ -0,0 +1,19 @@
+context 'when async suggestions are enabled' do
+  let(:options) { ["ZSH_AUTOSUGGEST_USE_ASYNC="] }
+
+  describe 'the zpty for async suggestions' do
+    it 'is created with the default name' do
+      session.run_command('zpty -t zsh_autosuggest_pty &>/dev/null; echo $?')
+      wait_for { session.content }.to end_with("\n0")
+    end
+
+    context 'when ZSH_AUTOSUGGEST_ASYNC_PTY_NAME is set' do
+      let(:options) { super() + ['ZSH_AUTOSUGGEST_ASYNC_PTY_NAME=foo_pty'] }
+
+      it 'is created with the specified name' do
+        session.run_command('zpty -t foo_pty &>/dev/null; echo $?')
+        wait_for { session.content }.to end_with("\n0")
+      end
+    end
+  end
+end