Fixes RC4 config dependencies in tests in ssl-opt.h

Adds dependencies on MBEDTLS_REMOVE_ARC4_CIPHERSUITES for tests that
require RC4 to be disabled (the default config).
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 8f49e96..103809b 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -567,12 +567,14 @@
 
 # Tests for rc4 option
 
+requires_config_enabled MBEDTLS_REMOVE_ARC4_CIPHERSUITES
 run_test    "RC4: server disabled, client enabled" \
             "$P_SRV" \
             "$P_CLI force_ciphersuite=TLS-RSA-WITH-RC4-128-SHA" \
             1 \
             -s "SSL - The server has no ciphersuites in common"
 
+requires_config_enabled MBEDTLS_REMOVE_ARC4_CIPHERSUITES
 run_test    "RC4: server half, client enabled" \
             "$P_SRV arc4=1" \
             "$P_CLI force_ciphersuite=TLS-RSA-WITH-RC4-128-SHA" \