Revert r188531: "Windows ToolChain: add VS bin dir to PogramPaths"

This never really worked. Even if we find and execute link.exe in the VS bin dir
this way, link.exe wouldn't find the DLLs it needs, libraries, etc.

It also causes trouble when the user has multiple versions of VS installed,
one of them is in the path, but this code finds the other one (PR17041).

Revert until we can fix this properly.

> Windows ToolChain: add VS bin dir to PogramPaths
>
> We have a lot of fancy logic to find Visual Studio, which is currently used
> to set the system header include paths.
>
> Use the same code to set the ProgramPaths, which is used for finding programs
> such as link.exe. Previously, Clang would just search PATH for link.exe,
> but now it should find it if it's able to find Visual Studio.