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/IRect_045.cpp b/docs/examples/IRect_045.cpp
index 0d1ea1f..60e8a3f 100644
--- a/docs/examples/IRect_045.cpp
+++ b/docs/examples/IRect_045.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=c00ef06289d21db70340e465690e0e08
-REG_FIDDLE(IRect_045, 256, 256, true, 0) {
+REG_FIDDLE(IRect_join, 256, 256, true, 0) {
 void draw(SkCanvas* canvas) {
     SkIRect rect = { 10, 20, 15, 25};
     rect.join(50, 60, 55, 65);