Revert of Add visualbench as valid target to Makefile (patchset #2 id:20001 of https://codereview.chromium.org/1530233005/ )

Reason for revert:
might be breaking cmakebot

Original issue's description:
> Add visualbench as valid target to Makefile
>
> BUG=skia:
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1530233005
>
> Committed: https://skia.googlesource.com/skia/+/13221b83663778a2f5cbd90e51e253268755877e

TBR=borenet@google.com,joshualitt@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1537903003
diff --git a/Makefile b/Makefile
index 2a24155..695ff77 100644
--- a/Makefile
+++ b/Makefile
@@ -41,7 +41,6 @@
 # world.
 VALID_TARGETS := \
                  nanobench \
-                 visualbench \
                  debugger \
                  dm \
                  everything \