caps: No need to require writable caps for _append/_merge second caps
caps: No need to require writable caps for _append/_merge second caps

The second caps ownership is transfered, no need to require it to
be writable from the caller function. Instead, _append and _merge
make it writable on their own.

Discovered because of an assertion on encoding-profile.c in
_get_input_caps using _merge but not passing writable caps.

mparis/gstreamer,centricular/gstreamer,jpakkane/gstreamer,Lachann/gstreamer,cablelabs/gstreamer,cfoch/gstreamer,justinjoy/gstreamer,krieger-od/gstreamer,cfoch/gstreamer,ylatuya/gstreamer,StreamUtils/gstreamer,ensonic/gstreamer,ensonic/gstreamer,collects/gstreamer,surround-io/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer,cfoch/gstreamer,justinjoy/gstreamer,StreamUtils/gstreamer,mparis/gstreamer,Lachann/gstreamer,cablelabs/gstreamer,lovebug356/gstreamer,ensonic/gstreamer,cablelabs/gstreamer,ylatuya/gstreamer,cablelabs/gstreamer,collects/gstreamer,lubosz/gstreamer,justinjoy/gstreamer,drothlis/gstreamer,collects/gstreamer,surround-io/gstreamer,Distrotech/gstreamer,lovebug356/gstreamer,shelsonjava/gstreamer,collects/gstreamer,krieger-od/gstreamer,drothlis/gstreamer,justinjoy/gstreamer,Distrotech/gstreamer,krichter722/gstreamer,drothlis/gstreamer,shelsonjava/gstreamer,ylatuya/gstreamer,jpakkane/gstreamer,lovebug356/gstreamer,ensonic/gstreamer,Lachann/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,StreamUtils/gstreamer,surround-io/gstreamer,centricular/gstreamer,krieger-od/gstreamer,Lachann/gstreamer,ylatuya/gstreamer,mparis/gstreamer,drothlis/gstreamer,lovebug356/gstreamer,centricular/gstreamer,krichter722/gstreamer,jpakkane/gstreamer,krieger-od/gstreamer,jpakkane/gstreamer,cablelabs/gstreamer,drothlis/gstreamer,StreamUtils/gstreamer,jpakkane/gstreamer,krichter722/gstreamer,cfoch/gstreamer,cfoch/gstreamer,ensonic/gstreamer,jpxiong/gstreamer,krieger-od/gstreamer,Lachann/gstreamer,lubosz/gstreamer,Distrotech/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,centricular/gstreamer,justinjoy/gstreamer,surround-io/gstreamer,lubosz/gstreamer,Distrotech/gstreamer,ylatuya/gstreamer,centricular/gstreamer,lubosz/gstreamer,mparis/gstreamer,surround-io/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer,lovebug356/gstreamer,mparis/gstreamer,Distrotech/gstreamer,collects/gstreamer,lubosz/gstreamer