libsframe: testsuite: use SFrame V2 specific APIs

Use sframe_encoder_add_funcdesc_v2 instead of sframe_encoder_add_funcdesc.
Similarly, use sframe_decoder_get_funcdesc_v2 instead of
sframe_decoder_get_funcdesc.

sframe_encoder_add_funcdesc, and sframe_decoder_get_funcdesc were first
added for SFrame V1.  For the purpose of these testcases, the two V2
APIs are (almost) functionally equivalent.  In future, we may want to
make sframe_encoder_add_funcdesc and sframe_decoder_get_funcdesc
internal to libsframe only.  Using the V2 named APIs is better for
clarity as well.

libsframe/testsuite/
	* libsframe.encode/encode-1.c: Use V2 named APIs instead.
	* libsframe.find/findfre-1.c: Likewise.
	* libsframe.find/findfunc-1.c: Likewise.
	* libsframe.decode/be-flipping.c: Likewise.
	* libsframe.decode/frecnt-1.c: Likewise.
	* libsframe.decode/frecnt-2.c: Likewise.