cert_create: Remove references to TBBR in common code

In preparation of supporting alternate chains of trust, reword comments
and error messages that explicitly mentioned TBBR.

Change-Id: I85a0b08e16d0cd82f3b767fcc092d1f20f45939f
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
diff --git a/tools/cert_create/src/main.c b/tools/cert_create/src/main.c
index 863db7b..2ba1101 100644
--- a/tools/cert_create/src/main.c
+++ b/tools/cert_create/src/main.c
@@ -47,7 +47,7 @@
 	do { \
 		v = OBJ_txt2nid(oid); \
 		if (v == NID_undef) { \
-			ERROR("Cannot find TBB extension %s\n", oid); \
+			ERROR("Cannot find extension %s\n", oid); \
 			exit(1); \
 		} \
 	} while (0)
@@ -335,7 +335,7 @@
 
 	/* Initialize the new types and register OIDs for the extensions */
 	if (ext_init() != 0) {
-		ERROR("Cannot initialize TBB extensions\n");
+		ERROR("Cannot initialize extensions\n");
 		exit(1);
 	}