drm/amd/display: Remove redundant header files

The header file "dc_stream.h" is already included on line 1507. Remove the
redundant include.

This is because the header file was initially included towards the latter
part of the code. Subsequent commits had to include the header file again
earlier in the code. In my opinion, this doesn't count as a fix; it just
requires removing the redundant header inclusion.

Signed-off-by: Liao Yuanhong <liaoyuanhong@vivo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>