only available in buildbot 8.6 and newer

Revert "buildbot: add new ForceScheduler for mingwlibs to force its branch to master"

This reverts commit 9a6fc1e.

buildbot/master/master.cfg

@@ -90,7 +90,6 @@ def changeIsImportant(change):
 
 from buildbot.changes.filter import ChangeFilter
 from buildbot.schedulers import basic, timed
-from buildbot.schedulers.forcesched import *
 
 c['schedulers'].append(basic.AnyBranchScheduler(
 	name="full-sched",
@@ -106,11 +105,6 @@ c['schedulers'].append(timed.Nightly(
 	onlyIfChanged=True,
 	builderNames=["cppcheck", "doxygen", "full-macosx", "latest-boost"], hour=6, minute=0))
 
-c['schedulers'].append(ForceScheduler(
-	name="force",
-	branch="master",
-	builderNames=["mingwlibs"]))
-
 ####### BUILDERS
 
 from buildbot.process.factory import BuildFactory