Revert "Make OpenJDK 8 the default"

Temporary revert to help out Brillo folks.
It will be resubmitted tomorrow.

This reverts commit 4495f6afb8c23950c24dc9ee114050582da08f05.

Change-Id: Id378c7d3a6e72e9be50f9404b19d5763568987a5
diff --git a/envsetup.sh b/envsetup.sh
index 61b9ff0..f266f1a 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -1426,8 +1426,7 @@
     fi
 
     if [ ! "$JAVA_HOME" ]; then
-      if [ -n "$LEGACY_USE_JAVA7" ]; then
-        echo Warning: Support for JDK 7 will be dropped. Switch to JDK 8.
+      if [ ! "$EXPERIMENTAL_USE_JAVA8" ]; then
         case `uname -s` in
             Darwin)
                 export JAVA_HOME=$(/usr/libexec/java_home -v 1.7)