decproxy2: remove creation of fake src caps
decproxy2: remove creation of fake src caps

Fake decoder has a role for creating fake src caps, so decproxy deos not
need to make it anymore.

Change-Id: Ia7baa522114bfffe80f38c454632ef1e5c5cb05d
Reviewed-on: https://gpro.lgsvl.com/74992
Tested-by: Wonchul Lee <9841bdbec9dbb2acc2dcaaa1dab0491399f0e464@lge.com>
Reviewed-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>
Tested-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>

justinjoy/gst-plugins-cool,justinjoy/gst-plugins-cool