Remove references to disposed SQLAlchemy engines from instrumentation singleton (#3053)

* Remove references to SQLAlchemy engines which are disposed of

EngineTracer in SQLAlchemy keeps weak references to a traced engine forever which
can cause a noticeable memory leak if engines are constantly getting creating.

* Updated changelog

---------

Co-authored-by: Emídio Neto <9735060+emdneto@users.noreply.github.com>
Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>

instrumentation/opentelemetry-instrumentation-sqlalchemy/tests/test_sqlalchemy.py

@@ -417,6 +417,10 @@ class TestSqlalchemyInstrumentation(TestBase):
 
         from sqlalchemy import create_engine
 
+        from opentelemetry.instrumentation.sqlalchemy.engine import (
+            EngineTracer,
+        )
+
         callback = mock.Mock()
 
         def make_shortlived_engine():
@@ -432,3 +436,4 @@ class TestSqlalchemyInstrumentation(TestBase):
 
         gc.collect()
         assert callback.call_count == 5
+        assert len(EngineTracer._remove_event_listener_params) == 0