codec: replace GSM-FR ECU with new implementation

The original GSM-FR ECU implementation from 2017 exhibits a lot of
defects, as detailed in OS#6027.  Replace it with a new implementation
based on Themyscira libgsmfrp (a complete Rx DTX handler for GSM-FR),
but reduced to just the ECU function, without the comfort noise
generator function.  (These two functions are coupled together in the
classic GSM architecture, but not in libosmocodec ECU model.)

Related: OS#6027
Change-Id: I0200e423ca6165c1313ec9a4effc3f3047f5f032
diff --git a/tests/codec/codec_ecu_fr_test.c b/tests/codec/codec_ecu_fr_test.c
index a9dae89..4e5b71d 100644
--- a/tests/codec/codec_ecu_fr_test.c
+++ b/tests/codec/codec_ecu_fr_test.c
@@ -151,7 +151,7 @@
 	int i, rc;
 	int j = 0;
 
-	printf("=> Testing FR concealment (simple, consecutive bad frames)\n");
+	printf("=> Testing FR concealment (simple, using ECU abstraction)\n");
 
 	while (sample_frame_hex[j] != NULL) {
 		/* Parse frame from string to hex */