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/Region_031.cpp b/docs/examples/Region_031.cpp
index 0fa3391..c16548b 100644
--- a/docs/examples/Region_031.cpp
+++ b/docs/examples/Region_031.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=5b31a1b077818a8150ad50f3b19e7bfe
-REG_FIDDLE(Region_031, 256, 256, true, 0) {
+REG_FIDDLE(Region_setRect_2, 256, 256, true, 0) {
 void draw(SkCanvas* canvas) {
     auto debugster = [](const char* label, bool success, SkRegion& region) -> void {
         auto r = region.getBounds();