don't use bashism just to remove trailing ':'

Change-Id: I9f86baa65406ac547cee70a273eb730ca47df66b

envsetup.sh

@@ -100,8 +100,9 @@ function setpaths()
         export PATH=${PATH/$ANDROID_BUILD_PATHS/}
     fi
     if [ -n $ANDROID_PRE_BUILD_PATHS ] ; then
-        shopt -s extglob
-        export PATH=${PATH/$ANDROID_PRE_BUILD_PATHS?(:)/}
+        export PATH=${PATH/$ANDROID_PRE_BUILD_PATHS/}
+        # strip trailing ':', if any
+        export PATH=${PATH/%:/}
     fi
 
     # and in with the new