docs: remove reference to OGI and rephrase sections docs
docs: remove reference to OGI and rephrase sections docs

The OGI links are dead, so remove them. Also remove the paragraph that pointed
to OGI and DS. Only mentioning DS there made it a but pointless. Add a generic
paragraph instead that tells a bit about the usecases gstreamer covers.

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