scripts/oe-buildenv-internal: improve the error detecting for $BDIR

scripts/oe-buildenv-internal: improve the error detecting for $BDIR

The previous fix for a bug in Ubuntu 10.04 readlink,
be2a2764d8ceb398d81714661e6f199c8b11946c, notified the user when a trailing
slash was used. As there is no semantic difference, simply remove any
trailing slashes and proceed without nagging the user.

See [YOCTO #671] for more details.

(From OE-Core rev: 074ca832c0274e0e92698b4d006ef2708be105b8)

Signed-off-by: Dexuan Cui <dexuan.cui@intel.com>
Acked-by: Darren Hart <dvhart@linux.intel.com>
Cc: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>