git cl try: default testfilter is no testfilter.
git cl try: default testfilter is no testfilter.

This removes default testfilter value ['defaulttests'] from polluting properties
everywhere.

This also implies that default testfilter is no testfilter or empty list, which
should have equivalent meening in try recipes.

R=phajdan.jr@chromium.org,nodir@chromium.org
BUG=487822

Review URL: https://codereview.chromium.org/1423483002

git-svn-id: fd409f4bdeea2bb50a5d34bb4d4bfc2046a5a3dd@297228 0039d316-1c4b-4281-b951-d872f2087c98

duongbaoduy/gtools,CoherentLabs/depot_tools,primiano/depot_tools,disigma/depot_tools,duongbaoduy/gtools,aleonliao/depot_tools,aleonliao/depot_tools,disigma/depot_tools,duanwujie/depot_tools,azureplus/chromium_depot_tools,duanwujie/depot_tools,hsharsha/depot_tools,CoherentLabs/depot_tools,duongbaoduy/gtools,aleonliao/depot_tools,hsharsha/depot_tools,azureplus/chromium_depot_tools,primiano/depot_tools,azureplus/chromium_depot_tools,primiano/depot_tools,duanwujie/depot_tools,disigma/depot_tools,hsharsha/depot_tools