Remove openssl from grpc.pc because we do not ship openssl.pc in base system

--- CMakeLists.txt.orig	2021-06-19 00:53:16 UTC
+++ CMakeLists.txt
@@ -15696,7 +15696,7 @@ generate_pkgconfig(
   "gRPC"
   "high performance general RPC framework"
   "${gRPC_CORE_VERSION}"
-  "gpr openssl absl_base absl_bind_front absl_flat_hash_map absl_inlined_vector absl_memory absl_optional absl_status absl_statusor absl_str_format absl_strings absl_synchronization absl_time"
+  "gpr absl_base absl_bind_front absl_flat_hash_map absl_inlined_vector absl_memory absl_optional absl_status absl_statusor absl_str_format absl_strings absl_synchronization absl_time"
   "-lgrpc -laddress_sorting -lre2 -lupb -lcares -lz"
   ""
   "grpc.pc")