soong_ui: Do not clean the OutDir path multiple times.

If OUT_DIR has been specified through the command line arguments,
it is sanitized first and NewConfig sets the OUT_DIR in the build
environment. When calling OutDir from Config instance, the out
was being sanitized again which is unnecessary.

Bug: b/118730755
Test: Ran unit test cases, "lunch" followed by "m" command.
Change-Id: Ieb4ffa1026c802c76c7369e8cdb3923a4c70f4b3