Remove heat-slow tox entry

The heat-slow tox entry tries to run 0 tests at the
moment.

Change-Id: I582c697d59d121bdd43d9c41eeba1b67c64a4861
diff --git a/tox.ini b/tox.ini
index 88d1302..b89f1ce 100644
--- a/tox.ini
+++ b/tox.ini
@@ -59,16 +59,6 @@
   find . -type f -name "*.pyc" -delete
   bash tools/pretty_tox_serial.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty)) {posargs}'
 
-[testenv:heat-slow]
-sitepackages = {[tempestenv]sitepackages}
-setenv = {[tempestenv]setenv}
-         OS_TEST_TIMEOUT=1200
-deps = {[tempestenv]deps}
-# The regex below is used to select heat api/scenario tests tagged as slow.
-commands =
-  find . -type f -name "*.pyc" -delete
-  bash tools/pretty_tox.sh '(?=.*\[.*\bslow\b.*\])(^tempest\.(api|scenario)\.orchestration) {posargs}'
-
 [testenv:large-ops]
 sitepackages = {[tempestenv]sitepackages}
 setenv = {[tempestenv]setenv}