DOC: Remove "Multiple lines using pyplot"

We should not promote the specific `plot(x, y, fmt, x2, y2, fmt)` anymore. This is a Matlabism and hard to read and reason about. Separate `plot()` calls are the better option. They don't need a dedicated pyplot example. Therefore, a redirect to the pyplot subplot example is sufficient, which as a side-topic has two plot calls in one subplot.

Author: timhoffm

galleries/examples/pyplots/pyplot_three.py

@@ -3,7 +3,16 @@
 Two subplots using pyplot
 =========================
 
-Create a figure with two subplots using `.pyplot.subplot`.
+In pyplot, subplots are created incrementally through `~.pyplot.subplot`.
+The three-digit number passed to `~.pyplot.subplot` specifies the position of
+the subplot in the grid of subplots. ``211`` means "in a grid of 2 rows and 1 column,
+create this subplot in the 1st position". ``212`` likewise means "in a grid of 2
+rows and 1 column, create this subplot in the 2nd position".
+
+After calling ``subplot()`` all following pyplot commands will modify that subplot
+until a new subplot is created.
+
+.. redirect-from:: /gallery/pyplots/pyplot_three
 """
 
 import matplotlib.pyplot as plt
@@ -21,9 +30,11 @@ def f(t):
 plt.subplot(211)
 plt.plot(t1, f(t1), color='tab:blue', marker='o')
 plt.plot(t2, f(t2), color='black')
+plt.title("Supblot 1")
 
 plt.subplot(212)
 plt.plot(t2, np.cos(2*np.pi*t2), color='tab:orange', linestyle='--')
+plt.title("Subplot 2")
 plt.show()
 
 # %%