Fix the ConPTY extended attributes optimization (#13661)

... which should have never worked in the first place


Quick filing a PR for review. This is the bulk of the actual code changes. Figured it was best to review the conpty changes sooner than later and I can add tests in the morning.

Test cases:
```
printf "\e[7m         test         \e[m\n"
```

```
printf "\e[7m"; printf ' %.0s' $(seq 1 $COLUMNS); printf "\e[m\n"
```

After:
![image](https://user-images.githubusercontent.com/18356694/182478185-6e65ab99-5c27-4772-af3b-2baa22387ec1.png)


Closes #13229


Definitely fixes:
* [x] #13643
* [x] https://github.com/PowerShell/PowerShell/issues/17812

src/buffer/out/TextAttribute.cpp

@@ -357,11 +357,6 @@ void TextAttribute::SetReverseVideo(bool isReversed) noexcept
     WI_UpdateFlag(_wAttrLegacy, COMMON_LVB_REVERSE_VIDEO, isReversed);
 }
 
-ExtendedAttributes TextAttribute::GetExtendedAttributes() const noexcept
-{
-    return _extendedAttrs;
-}
-
 // Routine Description:
 // - swaps foreground and background color
 void TextAttribute::Invert() noexcept