api: remove unused singular option

The singular option to the API language was added as a way to deal with messages
that do not have a reply message. Examples in memclnt.api.
Instead dealt with these messages using the service {} construct.

Type: refactor
Signed-off-by: Ole Troan <ot@cisco.com>
Change-Id: If01b390b24b7539d1f93de4b8edfe1dad08e509d
diff --git a/src/tools/vppapigen/vppapigen.py b/src/tools/vppapigen/vppapigen.py
index b80dd4d..0782dd2 100755
--- a/src/tools/vppapigen/vppapigen.py
+++ b/src/tools/vppapigen/vppapigen.py
@@ -308,7 +308,6 @@
         self.manual_print = False
         self.manual_endian = False
         self.autoreply = False
-        self.singular = False
         self.options = {}
         for f in flags:
             if f == 'dont_trace':
@@ -323,10 +322,7 @@
         remove = []
         for b in block:
             if isinstance(b, Option):
-                if b[1] == 'singular' and b[2] == 'true':
-                    self.singular = True
-                else:
-                    self.options[b.option] = b.value
+                self.options[b.option] = b.value
                 remove.append(b)
 
         block = [x for x in block if x not in remove]
@@ -1042,8 +1038,6 @@
         for d in msgs:
             if d in seen_services:
                 continue
-            if msgs[d].singular is True:
-                continue
             if d.endswith('_reply'):
                 if d[:-6] in svcs:
                     continue