src: remove unused env strings
user_string: Usage removed in 4e05952a onstop_string: Usage removed in 7b46e177 max_old_space_size_string: Added in 0df031ac, never used max_semi_space_size_string: Added in 0df031ac, never used enter_string: Usage removed in eeede3b1
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines