[composer] Remove implication.

The spec of setLayerDataspace never specifies the types of layer it should be
call on, however, the spec has the implication that this method will only work
for layers with buffer, which is mis-leading. This patch changes the wording of
setLayerDataspace spec, removes the implication. Note that this change won't
break backward compatability.

BUG: 126713799
Test: N/A
Change-Id: I97f22469897cb687dcb64a3d419bcb48a3668e5a