envsetup: avoid adding "::" (the cwd) to the PATH

Fix this error:

    rprichard@cashew:/x/aosp/out/target/product/walleye/system/bin$ ls
    bash: ./ls: cannot execute binary file: Exec format error

Bug: none
Test: lunch a target, "echo $PATH | grep ::"
Test: lunch an arm target, cd $OUT/system/bin, ls (
Change-Id: I2c0d5ece85964dffa14d6ac8df168dd4e733162e
diff --git a/envsetup.sh b/envsetup.sh
index 941c5f7..9198ee5 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -272,12 +272,12 @@
 
     # Append asuite prebuilts path to ANDROID_BUILD_PATHS.
     local os_arch=$(get_build_var HOST_PREBUILT_TAG)
-    local ACLOUD_PATH="$T/prebuilts/asuite/acloud/$os_arch:"
-    local AIDEGEN_PATH="$T/prebuilts/asuite/aidegen/$os_arch:"
-    local ATEST_PATH="$T/prebuilts/asuite/atest/$os_arch:"
-    export ANDROID_BUILD_PATHS=$ANDROID_BUILD_PATHS:$ACLOUD_PATH$AIDEGEN_PATH$ATEST_PATH
+    local ACLOUD_PATH="$T/prebuilts/asuite/acloud/$os_arch"
+    local AIDEGEN_PATH="$T/prebuilts/asuite/aidegen/$os_arch"
+    local ATEST_PATH="$T/prebuilts/asuite/atest/$os_arch"
+    export ANDROID_BUILD_PATHS=$ANDROID_BUILD_PATHS:$ACLOUD_PATH:$AIDEGEN_PATH:$ATEST_PATH:
 
-    export PATH=$ANDROID_BUILD_PATHS:$PATH
+    export PATH=$ANDROID_BUILD_PATHS$PATH
 
     # out with the duplicate old
     if [ -n $ANDROID_PYTHONPATH ]; then