TST don't collect tests from deprecated modules.

This removes some deprecation warnings in tests.

conftest.py

@@ -4,7 +4,15 @@
 
 from scrapy import optional_features
 
-collect_ignore = ["scrapy/stats.py", "scrapy/project.py"]
+collect_ignore = [
+    "scrapy/conf.py",
+    "scrapy/stats.py",
+    "scrapy/project.py",
+    "scrapy/contrib_exp/__init__.py",
+    "scrapy/contrib_exp/iterators.py",
+    "scrapy/contrib_exp/downloadermiddleware/__init__.py",
+    "scrapy/contrib_exp/downloadermiddleware/decompression.py",
+]
 if 'django' not in optional_features:
     collect_ignore.append("tests/test_djangoitem/models.py")
 
@@ -14,6 +22,7 @@
         if len(file_path) > 0 and file_path[0] != '#':
             collect_ignore.append(file_path)
 
+
 class LogObservers:
     """Class for keeping track of log observers across test modules"""