[server] Drop inexistent "bootstrap" argument in Repository initialization This is a missing bit from 5de78b6fff2e. Unfortunately this code appears to be uncovered by our test suite.

pytest
http://hg.logilab.org/master/logilab/common/archive/default.tar.bz2#egg=logilab-common
http://hg.logilab.org/master/yams/archive/default.tar.bz2#egg=yams