[introspection] Disable constructors for now

Since our types are not associated with their methods, marking
constructors makes them inaccessible from bindings.  Undo for now.

src/hb-blob.cc

@@ -77,7 +77,7 @@ _hb_blob_destroy_user_data (hb_blob_t *blob)
 }
 
 /**
- * hb_blob_create: (constructor)
+ * hb_blob_create: (Xconstructor)
  * @data: (array length=length): Pointer to blob data.
  * @length: Length of @data in bytes.
  * @mode: Memory mode for @data.

src/hb-buffer.cc

@@ -604,7 +604,7 @@ void hb_buffer_t::deallocate_var_all (void)
 /* Public API */
 
 /**
- * hb_buffer_create: (constructor)
+ * hb_buffer_create: (Xconstructor)
  *
  * 
  *

src/hb-face.cc

@@ -150,7 +150,7 @@ _hb_face_for_data_reference_table (hb_face_t *face HB_UNUSED, hb_tag_t tag, void
 }
 
 /**
- * hb_face_create: (constructor)
+ * hb_face_create: (Xconstructor)
  * @blob: 
  * @index: 
  *

src/hb-font.cc

@@ -231,7 +231,7 @@ static const hb_font_funcs_t _hb_font_funcs_nil = {
 
 
 /**
- * hb_font_funcs_create: (constructor)
+ * hb_font_funcs_create: (Xconstructor)
  *
  * 
  *
@@ -839,7 +839,7 @@ hb_font_glyph_from_string (hb_font_t *font,
  */
 
 /**
- * hb_font_create: (constructor)
+ * hb_font_create: (Xconstructor)
  * @face: a face.
  *
  * 

src/hb-set.cc

@@ -31,7 +31,7 @@
 
 
 /**
- * hb_set_create: (constructor)
+ * hb_set_create: (Xconstructor)
  *
  * Return value: (transfer full):
  *

src/hb-shape-plan.cc

@@ -84,7 +84,7 @@ hb_shape_plan_plan (hb_shape_plan_t    *shape_plan,
  */
 
 /**
- * hb_shape_plan_create: (constructor)
+ * hb_shape_plan_create: (Xconstructor)
  * @face: 
  * @props: 
  * @user_features: (array length=num_user_features):

src/hb-unicode.cc

@@ -151,7 +151,7 @@ hb_unicode_funcs_get_default (void)
 #endif
 
 /**
- * hb_unicode_funcs_create: (constructor)
+ * hb_unicode_funcs_create: (Xconstructor)
  * @parent: (allow-none):
  *
  *