Fixed sys usage (#916)

Just as a heads up, I haven't really tested this since a lot of it is
stuff I don't use or know how to set up without some reading up. I have
tested the nu_conda_2 change since I have a python project that I use
that for, and I could look into testing more of it if needed.

I've tried finding (naively using `/sys\W/`) all the usage of the old
plain `sys` calls and replacing them with alternates as appropriate,
which mostly has been to swap a `(sys).host.name` call into a
`$nu.os-info.name` one, since it'll be tad faster and more consistent
across platforms with naming (especially as the value comes from the
[rust stdlib](https://doc.rust-lang.org/std/env/consts/constant.OS.html)
and is very predictable).

Fixes #897

modules/weather/timed_weather_run.nu

@@ -18,10 +18,7 @@ def timed_weather_run [
     --interval(-i): duration # The interval duration
     ] {
 
-    # get the type of system we're on
-    let system_name = ((sys).host | get name)
-
-    if $system_name == "Windows" {
+    if $nu.os-info.name == "windows" {
         # $"The system is Windows(char nl)"
         # generate temp file name
         let weather_runtime_file = (($env.TMP) | path join weather_runtime_file.json)