Drop unnecessary Blinker dependency

[jeffwidman]

Flask requires this, so it's a transitive dep, but it's not directly used within this toolbar at all.

We do directly import the other listed packages, so they should stay.

[jeffwidman]

Oh interesting, Python 3.7 requires Blinker...

Probably newer Flasks require it, but Flask 2.2.0 doesn't... not worth tracking down, but essentially this PR is blocked until we drop Python 3.7 support.

=================================== FAILURES ===================================
________________________________ test_basic_app ________________________________

    def test_basic_app():
        app = load_app('basic_app')
>       index = app.get('/')

test/test_toolbar.py:14: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
.tox/py[37](https://github.com/pallets-eco/flask-debugtoolbar/actions/runs/8809300665/job/24179876713?pr=248#step:6:38)/lib/python3.7/site-packages/werkzeug/test.py:1141: in get
    return self.open(*args, **kw)
.tox/py37/lib/python3.7/site-packages/flask/testing.py:2[41](https://github.com/pallets-eco/flask-debugtoolbar/actions/runs/8809300665/job/24179876713?pr=248#step:6:42): in open
    follow_redirects=follow_redirects,
.tox/py37/lib/python3.7/site-packages/werkzeug/test.py:1095: in open
    response = self.run_wsgi_app(request.environ, buffered=buffered)
.tox/py37/lib/python3.7/site-packages/werkzeug/test.py:962: in run_wsgi_app
    rv = run_wsgi_app(self.application, environ, buffered=buffered)
.tox/py37/lib/python3.7/site-packages/werkzeug/test.py:12[43](https://github.com/pallets-eco/flask-debugtoolbar/actions/runs/8809300665/job/24179876713?pr=248#step:6:44): in run_wsgi_app
    app_rv = app(environ, start_response)
.tox/py37/lib/python3.7/site-packages/flask/app.py:2552: in __call__
    return self.wsgi_app(environ, start_response)
.tox/py37/lib/python3.7/site-packages/flask/app.py:2532: in wsgi_app
    response = self.handle_exception(e)
.tox/py37/lib/python3.7/site-packages/flask/app.py:2529: in wsgi_app
    response = self.full_dispatch_request()
.tox/py37/lib/python3.7/site-packages/flask/app.py:1825: in full_dispatch_request
    rv = self.handle_user_exception(e)
.tox/py37/lib/python3.7/site-packages/flask/app.py:1821: in full_dispatch_request
    rv = self.preprocess_request()
.tox/py37/lib/python3.7/site-packages/flask/app.py:2313: in preprocess_request
    rv = self.ensure_sync(before_func)()
.tox/py37/lib/python3.7/site-packages/flask_debugtoolbar/__init__.py:175: in process_request
    DebugToolbar(real_request, self.jinja_env))
.tox/py37/lib/python3.7/site-packages/flask_debugtoolbar/toolbar.py:23: in __init__
    self.create_panels()
.tox/py37/lib/python3.7/site-packages/flask_debugtoolbar/toolbar.py:34: in create_panels
    context=self.template_context)
.tox/py37/lib/python3.7/site-packages/flask_debugtoolbar/panels/template.py:37: in __init__
    template_rendered.connect(self._store_template_info)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <flask.signals._FakeSignal object at 0x7f2093568ed0>
args = (<bound method TemplateDebugPanel._store_template_info of <flask_debugtoolbar.panels.template.TemplateDebugPanel object at 0x7f20920ab8[50](https://github.com/pallets-eco/flask-debugtoolbar/actions/runs/8809300665/job/24179876713?pr=248#step:6:51)>>,)
kwargs = {}

    def _fail(self, *args: t.Any, **kwargs: t.Any) -> t.Any:
        raise RuntimeError(
            "Signalling support is unavailable because the blinker"
            " library is not installed."
>       ) from None
E       RuntimeError: Signalling support is unavailable because the blinker library is not installed.

[jeffwidman]

We dropped 3.7 support:

• drop python 3.7 support #255

So this PR is unblocked... I've rebased it and it should be good to go.

[jeffwidman]

🤔 I wonder though... it seems the exception in #248 (comment) implies that we are directly relying on Blinker somehow... My guess is for signals, although I haven't tracked down whether FDBT is using signals all the time, or just in that particular test.

Regardless, now that we've dropped Python 3.7 support, the simpler thing might be to bump Flask to 2.3.0:

• Bump Flask to >=2.3.0 #256

[davidism]

I don't think we need any dependency except Flask itself. Declaring Flask's own dependencies here is redundant, and would presumably break anyway if Flask were to not depend on them anymore (not that it would do that).