Remove blinker from dependencies

(Redmine issue: #7632)

conf/requirements.pip

@@ -6,7 +6,6 @@ wtforms_sqlalchemy>=0.3,<1.0.0
 sqlalchemy>=1.4.47,<2.0.0
 alembic>=1.10.2,<2.0.0
 jinja2>=3.1.2,<3.2.0
-blinker>=1.5,<1.6
 bsddb3>=6.2.9,<6.3.0
 werkzeug>=2.2.3,<3.0.0
 flask>=2.2.3,<2.3.0