Bug 1593948 - Touch clobber in configure.py instead of clobber.py; r=firefox-build-system-reviewers,chmanchester

If configure is invoked manually, clobber.py is bypassed and the CLOBBER
file doesn't get touched. The clobber check in Makefile.in gets
triggered causing the build to stop.

Moving the objdir/CLOBBER file creation into configure.py should cause
it to be created regardless of how configure is invoked.

Depends on D53290

Differential Revision: https://phabricator.services.mozilla.com/D53291

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extra : moz-landing-system : lando