Remove OpenBMC specific .templateconf

Starting with 92b42cb, sourcing the build environment as described in
https://docs.yoctoproject.org/brief-yoctoprojectqs/index.html#building-your-image
no longer works without explicitly setting TEMPLATECONF somehow, because
the default, defined in .templateconf, was not updated when the
meta-phosphor template moved in bb789d5.

All off this, paired with the lack of complaining about the breakage
suggests that not very many OpenBMC developers source the build
environment in the way described by the Poky documentation.

For the remaining few, the usual workflow for creating a new build tree
looks like:

```sh
TEMPLATECONF=meta-foo/conf/templates/default source oe-init-build-env build-dir
```
and for using an existing build tree just:
```sh
source oe-init-build-env build-dir
```

In the latter case, .templateconf need only point to a valid template -
the template is only actually used when the build tree is created. Given
the irrelevency of the actual content, instead of pointing at the
template in meta-phosphor, just use the Poky .templateconf, which has a
better chance of being maintained and staying in sync in the long run.

Signed-off-by: Brad Bishop <[email protected]>
Change-Id: I1f44e1140cd40aac50745ffe1318ad2826717618

.templateconf

@@ -0,0 +1 @@
+poky/.templateconf