[docs] Remove g++ from brew install in dev_environment

Summary:
Related linear task: ENG-697

The g++ is not provided by the brew anymore. The brew install autoconf automake libtool curl make g++ unzip command produces a not found error.
We need to remove the g++ from the list because it's provided by the code CLI tools which is installed before this command and not present in the brew anymore.

Test Plan: Run brew install g++

Reviewers: benschac, jonringer-comm, karol-bisztyga, ashoat

Reviewed By: karol-bisztyga, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3118