fix build: remove unused variable

fix: "src/gprs/gprs_gmm_attach.c:240:6: error: unused variable ‘rc’"

introduced by

"gprs_gmm: Fix missing Security Command for 3G when attaching"
Change Id  I1e12b0a32e58c6f78dba7b548f7d7016567229db

Change-Id: I4837c10fed915c558a5374d448af813219087f36
diff --git a/src/gprs/gprs_gmm_attach.c b/src/gprs/gprs_gmm_attach.c
index 60c4398..6fdb3af 100644
--- a/src/gprs/gprs_gmm_attach.c
+++ b/src/gprs/gprs_gmm_attach.c
@@ -237,7 +237,6 @@
 {
 #ifdef BUILD_IU
 	struct sgsn_mm_ctx *ctx = fi->priv;
-	int rc = 0;
 
 	/* TODO: shouldn't this set always? not only when the integrity_active? */
 	if (ctx->iu.ue_ctx->integrity_active) {