Small cleanups to colorbar.

- `__scale = "manual"` doesn't exist anymore since d1c5a6a.
- Shorten Boundary/NoNorm inversion and norm._scale check.
- No need to define `x` well before its use point, and no need to make
  it an array explicitly.

lib/matplotlib/colorbar.py

@@ -1132,18 +1132,14 @@ def _mesh(self):
         norm = copy.deepcopy(self.norm)
         norm.vmin = self.vmin
         norm.vmax = self.vmax
-        x = np.array([0.0, 1.0])
         y, extendlen = self._proportional_y()
         # invert:
-        if (isinstance(norm, (colors.BoundaryNorm, colors.NoNorm)) or
-                (self.__scale == 'manual')):
-            # if a norm doesn't have a named scale, or we are not using a norm:
-            dv = self.vmax - self.vmin
-            y = y * dv + self.vmin
+        if isinstance(norm, (colors.BoundaryNorm, colors.NoNorm)):
+            y = y * (self.vmax - self.vmin) + self.vmin  # not using a norm.
         else:
             y = norm.inverse(y)
         self._y = y
-        X, Y = np.meshgrid(x, y)
+        X, Y = np.meshgrid([0., 1.], y)
         if self.orientation == 'vertical':
             return (X, Y, extendlen)
         else:
@@ -1183,8 +1179,8 @@ def _reset_locator_formatter_scale(self):
                 self._set_scale('function', functions=funcs)
             elif self.spacing == 'proportional':
                 self._set_scale('linear')
-        elif hasattr(self.norm, '_scale') and self.norm._scale is not None:
-            # use the norm's scale:
+        elif getattr(self.norm, '_scale', None):
+            # use the norm's scale (if it exists and is not None):
             self._set_scale(self.norm._scale)
         elif type(self.norm) is colors.Normalize:
             # plain Normalize: