scripts: Drop cleanup-workdir

scripts: Drop cleanup-workdir

This script appears broken and is actively breaking build directories.
For example, binutils-cross-i586 gets run do_fetch to do_populate_sysroot by:

$ oe-selftest -r devtool.DevtoolTests.test_devtool_virtual_kernel_modify

then:

$ oe-selftest -r oescripts.BuildhistoryDiffTests.test_buildhistory_diff

wipes out the contents of tmp/work/x86_64-linux/binutils-cross-i586/2.28-r0/
but does not wipe out the corresponding stamps, then:

$ oe-selftest -r runtime-test.Postinst.test_postinst_rootfs_and_boot

needs binutils-cross-i586:do_populate_lic and if and only if this is
unavailable from sstate, it fails since it thinks the source is already
unpacked when it isn't resulting in:

WARNING: binutils-cross-i586-2.28-r0 do_populate_lic: Could not copy license file /home/pokybuild/yocto-autobuilder/yocto-worker/nigh
tly-oe-selftest/build/build/tmp/work/x86_64-linux/binutils-cross-i586/2.28-r0/git/COPYING3.LIB to /home/pokybuild/yocto-autobuilder/yocto
-worker/nightly-oe-selftest/build/build/tmp/work/x86_64-linux/binutils-cross-i586/2.28-r0/license-destdir/binutils-cross-i586/COPYING3.LI
B: [Errno 2] No such file or directory: '/home/pokybuild/yocto-autobuilder/yocto-worker/nightly-oe-selftest/build/build/tmp/work/x86_64-l
inux/binutils-cross-i586/2.28-r0/git/COPYING3.LIB'
ERROR: binutils-cross-i586-2.28-r0 do_populate_lic: QA Issue: binutils-cross-i586: LIC_FILES_CHKSUM points to an invalid file: /home/
pokybuild/yocto-autobuilder/yocto-worker/nightly-oe-selftest/build/build/tmp/work/x86_64-linux/binutils-cross-i586/2.28-r0/git/COPYING3 [license-checksum]

and similar errors.

Its safer for users to wipe tmp than try and maintain scripts which try
to remove pieces of tmp and get it wrong so remove the script.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>