Removing redundant env var WITH_HDF5_SCORPIO in buildlib.spio

If HDF5_ROOT is already set as an env var, it is sufficient to turn
on the WITH_HDF5 CMake option for scorpio. Introducing a new env var
like WITH_HDF5_SCORPIO may lead to unnecessary confusion.

Additionally, for now, maintain the WITH_HDF5 CMake option as OFF by
default to prevent potential build errors with the default scorpio
1.4.2 submodule.

share/build/buildlib.spio

@@ -132,8 +132,10 @@ def buildlib(bldroot, installpath, case):
     # elif which_h5dump is not None:
     #     os.environ["HDF5"] = os.path.dirname(os.path.dirname(which_h5dump))
 
-    if "WITH_HDF5_SCORPIO" in os.environ:
-        cmake_opts += "-DWITH_HDF5:BOOL=ON "
+    # Before E3SM upgrades scorpio submodule to 1.5.0 or higher, keep WITH_HDF5
+    # CMake option OFF by default.
+    # if "HDF5_ROOT" in os.environ:
+    #    cmake_opts += "-DWITH_HDF5:BOOL=ON "
 
     # Same deal with libz and szip
     if "ZLIB_ROOT" in os.environ: