Docs: Give documentation examples better names

These names come from the bookmaker generated md files.

Also, delete ducplicated and empty examples.

A later CL will re-name the cpp files.

Change-Id: Ie365b9cc1cc705d010c674b9988b32c8307a0455
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201609
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
diff --git a/docs/examples/Matrix_010.cpp b/docs/examples/Matrix_010.cpp
index e33c48a..a31fd79 100644
--- a/docs/examples/Matrix_010.cpp
+++ b/docs/examples/Matrix_010.cpp
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
 #include "fiddle/examples.h"
 // HASH=7a234c96608fb7cb8135b9940b0b15f7
-REG_FIDDLE(Matrix_010, 256, 256, true, 0) {
+REG_FIDDLE(Matrix_preservesAxisAlignment, 256, 256, true, 0) {
 void draw(SkCanvas* canvas) {
     SkMatrix matrix;
     for (SkScalar angle: { 0, 90, 180, 270 } ) {