BLD: Use setuptools_scm version_file

setuptools_scm 8.0.0 introduced `version_file` as a replacement
for `write_to` in setup.py schemes to specify the location of
the version file.

setup.py

@@ -37,17 +37,11 @@
 CMDCLASS = {"clean": setuputils.CleanUp}
 
 
-def src(anypath):
-    root = os.path.dirname(__file__)
-    return os.path.abspath(os.path.join(root, anypath))
-
-
 skbuild.setup(
     name="xtgeo",
     description="XTGeo is a Python library for 3D grids, surfaces, wells, etc",
     use_scm_version={
-        "root": src(""),
-        "write_to": src("src/xtgeo/_theversion.py"),
+        "version_file": "src/xtgeo/_theversion.py",
     },
     long_description=README + "\n\n" + HISTORY,
     long_description_content_type="text/markdown",
@@ -107,8 +101,7 @@ def src(anypath):
     setuptools_setup(  # use setuptools version of setup
         name="xtgeo",
         use_scm_version={
-            "root": src(""),
-            "write_to": src("src/xtgeo/_theversion.py"),
+            "version_file": "src/xtgeo/_theversion.py",
         },
         packages=setuptools.find_packages(where="src"),
         package_dir={"": "src"},