configure: build oox with NSS backend by default

Because NSS libraries are dynamic and OpenSSL static, using NSS saves
1.5 MB in the oox library [even though it's not as 1337 apparently]:

-rwxrwxr-x. 1 ms ms  8889575  2. Nov 13:45 libooxlo.so.nss
-rwxrwxr-x. 1 ms ms  7773576  2. Nov 13:45 libooxlo.so.nss.stripped
-rwxrwxr-x. 1 ms ms 10340276  2. Nov 13:37 libooxlo.so.openssl
-rwxrwxr-x. 1 ms ms  9042216  2. Nov 13:37 libooxlo.so.openssl.stripped

Change-Id: I387496ae364acb1286d753d52f04924631136750

configure.ac

@@ -8785,13 +8785,9 @@ nss - Mozilla's Network Security Services (NSS)
         ;;
     esac
 else
-    if test "$enable_openssl" = "yes"; then
-        AC_DEFINE(USE_TLS_OPENSSL)
-        TLS=OPENSSL
-    else
-        AC_DEFINE(USE_TLS_NSS)
-        TLS=NSS
-    fi
+    # default to using NSS, it results in smaller oox lib
+    AC_DEFINE(USE_TLS_NSS)
+    TLS=NSS
 fi
 AC_MSG_RESULT([$TLS])
 AC_SUBST(TLS)