.gitignore: add /smoke_magicfolder/, delete obsolete stuff.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

.gitignore

@@ -26,7 +26,6 @@ zope.interface-*.egg
 /tmp*
 /*.patch
 /dist/
-/twisted/plugins/dropin.cache
 /tahoe-deps/
 /tahoe-deps.tar.gz
 /.coverage
@@ -34,3 +33,4 @@ zope.interface-*.egg
 /coverage-html/
 /miscaptures.txt
 /violations.txt
+/smoke_magicfolder/