Remove unused imports from grdview.py

Author: seisman

pygmt/src/grdview.py

@@ -1,17 +1,8 @@
 """
 grdview - Create a three-dimensional plot from a grid.
 """
-import contextlib
-
 from pygmt.clib import Session
-from pygmt.exceptions import GMTInvalidInput
-from pygmt.helpers import (
-    build_arg_string,
-    data_kind,
-    fmt_docstring,
-    kwargs_to_strings,
-    use_alias,
-)
+from pygmt.helpers import build_arg_string, fmt_docstring, kwargs_to_strings, use_alias
 
 __doctest_skip__ = ["grdview"]