populate_sdk_base/meta-environment: Remove overlap from the two

populate_sdk_base/meta-environment: Remove overlap from the two

Currently we have the horrible situation where meta-environment packages
the toolchain environment files and they get included in the SDK but are
broken, then, the SDK code overwrites them with good versions. This is
suboptimal.

This change fixes the code in meta-environment to create working
files and adds in the multilib support from populate_sdk_base, then
we remove the code in that base bbclass and rely on the packages
being installed if/as/when needed. This removes the duplication
and the broken versions of the files, hopefully making all well.

[YOCTO #6608]
[YOCTO #6613]

(From OE-Core rev: 063355e5965439c7b3253d692d7ab0ed1189d123)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>