REF/TST: Finish pytest idiom in parser tests

Adds more idiom to the following:

* parser/common --> parser/test_common
* parser/quoting --> parser/test_quoting
* parser/usecols --> parser/test_usecols
* parser/python_parser_only -->
parser/test_python_parser_only

Also deletes parser/test_parsers.

Builds off of pandas-devgh-23712.

Author: gfyoung

pandas/tests/io/parser/common.py

@@ -24,8 +24,7 @@ def read_csv(self, *args, **kwargs):
 
     def read_table(self, *args, **kwargs):
         kwargs = self.update_kwargs(kwargs)
-        with tm.assert_produces_warning(FutureWarning):
-            return read_table(*args, **kwargs)
+        return read_table(*args, **kwargs)
 
 
 class CParser(BaseParser):
@@ -43,7 +42,7 @@ class CParserLowMemory(CParser):
 
 class PythonParser(BaseParser):
     engine = "python"
-    float_precision_choices = []
+    float_precision_choices = [None]
 
 
 @pytest.fixture