Revert "gprs: Use RAND_bytes for p-tmsi"

The commit not compiling/linking should have been a strong
indicator that it has not been tested either.

This reverts commit 6cf0249dacc4ae46eb0857c007906c9a3f128a3e.
diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index dcc6842..f46a402 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -30,5 +30,4 @@
 			gsm_04_08_gprs.c sgsn_cdr.c sgsn_ares.c
 osmo_sgsn_LDADD = 	\
 			$(top_builddir)/src/libcommon/libcommon.a \
-			-lgtp $(OSMO_LIBS) $(LIBOSMOABIS_LIBS) $(LIBCARES_LIBS) \
-			$(LIBCRYPTO_LIBS) -lrt
+			-lgtp $(OSMO_LIBS) $(LIBOSMOABIS_LIBS) $(LIBCARES_LIBS) -lrt