Remove redundant "by default" from virtualenv section (#1397)
Remove redundant "by default" from virtualenv section (#1397)

The paragraph describing virtualenvs contained the following sentence: "By default, Conan does not modify by default the environment (...)". The second redundant "by default" was removed.
conan-io/docs,conan-io/docs,conan-io/docs,conan-io/docs