Revert "envsetup: Always look up JAVA_HOME path" ยท CyanogenMod/android_build@9f360cd

This breaks, if we have both jdk7 and jdk8 installed on same machine. This reverts commit bc9ae3d5c21915c165b2b2cb41d07e1573814254. Change-Id: Id0482d130d5306e797adfeeaeb2efbd1e25aa3ee