src: remove unused env variables in node_util

Currently the following compiler warnings are generated:
../src/node_util.cc:59:16:
warning: unused variable 'env' [-Wunused-variable]
  Environment* env = Environment::GetCurrent(args);
               ^
../src/node_util.cc:78:16:
warning: unused variable 'env' [-Wunused-variable]
  Environment* env = Environment::GetCurrent(args);
               ^
2 warnings generated.

This commit removes the two unused variables.

PR-URL: https://github.com/nodejs/node/pull/24820


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>