Revert "Update docs preview URL in presubmit"

This reverts commit 5c646cf10fd9f4db788d3993ea73093649306e80.

Reason for revert: I figured out how to make a preview in seconds,
as opposed to the minute that it used to be, so a special server
for previews isn't needed.

Original change's description:
> Update docs preview URL in presubmit
> 
> NoTry: true
> Bug: skia:
> Change-Id: Id5b374f707ac44770a5142f104202d6509410767
> Reviewed-on: https://skia-review.googlesource.com/129505
> Reviewed-by: Joe Gregorio <jcgregorio@google.com>
> Commit-Queue: Ravi Mistry <rmistry@google.com>

TBR=rmistry@google.com,jcgregorio@google.com

Change-Id: I1bbf557729ad4124e93c15f529c7369f68397892
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/129447
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 8e33390..f9747fa 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -37,7 +37,7 @@
 
 AUTHORS_FILE_NAME = 'AUTHORS'
 
-DOCS_PREVIEW_URL = 'https://preview.skia.org/?cl='
+DOCS_PREVIEW_URL = 'https://skia.org/?cl='
 GOLD_TRYBOT_URL = 'https://gold.skia.org/search?issue='
 
 # Path to CQ bots feature is described in https://bug.skia.org/4364