qapi: Fix to reject optional members with reserved names

check_type() fails to reject optional members with reserved names,
because it neglects to strip off the leading '*'.  Fix that.

The stripping in check_name_str() is now useless.  Drop.

Also drop the "no leading '*'" assertion, because valid_name.match()
ensures it can't fail.

Fixes: 9fb081e0b9
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210323094025.3569441-8-armbru@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>

tests/qapi-schema/reserved-member-u.err

@@ -0,0 +1,2 @@
+reserved-member-u.json: In struct 'Oops':
+reserved-member-u.json:7: 'data' member '*u' uses reserved name

tests/qapi-schema/reserved-member-u.json

@@ -4,5 +4,4 @@
 # This is true even for non-unions, because it is possible to convert a
 # struct to flat union while remaining backwards compatible in QMP.
 # TODO - we could munge the member name to 'q_u' to avoid the collision
-# BUG: not rejected
 { 'struct': 'Oops', 'data': { '*u': 'str' } }

tests/qapi-schema/reserved-member-u.out

@@ -1,14 +0,0 @@
-module ./builtin
-object q_empty
-enum QType
-    prefix QTYPE
-    member none
-    member qnull
-    member qnum
-    member qstring
-    member qdict
-    member qlist
-    member qbool
-module reserved-member-u.json
-object Oops
-    member u: str optional=True