adjustments based on code review comments

Author: michaelgrund

pygmt/datasets/samples.py

@@ -1,5 +1,5 @@
 """
-Functions to load sample data from the GMT tutorials.
+Functions to load sample data.
 """
 import pandas as pd
 from pygmt.src import which

pygmt/tests/test_datasets_tutorial.py renamed to pygmt/tests/test_datasets_samples.py

@@ -1,5 +1,5 @@
 """
-Test basic functionality for loading datasets for tutorials.
+Test basic functionality for loading sample datasets.
 """
 from pygmt.datasets import (
     load_japan_quakes,