Do not customize environment variables for tor anymore

We currently customizes the following environment variables on TorProcess.jsm:

• TOR_BROWSER_TOR_DATA_DIR: according to a comment, it was used by meek-client to find the location for its profile. Obfs4 client replaced it, we can delete the variable
• PATH on Windows: according to legacy/trac#10845 (closed) it was done to make OpenSSL avilable to PTs, but now PTs are written in Go and link only kernel32.dll. tor is also statically linked now (see tor-browser-build#40642).

So, let's declutter also this!