lib/tls: use python3 to run inline script

We only need to run this fixup for the active python now we are 3 only.

Change-Id: I7616e5ee5693b2890fb7f6bd9052890a82904c22
diff --git a/lib/tls b/lib/tls
index 65ffeb9..d05536b 100644
--- a/lib/tls
+++ b/lib/tls
@@ -369,8 +369,7 @@
 function fix_system_ca_bundle_path {
     if is_service_enabled tls-proxy; then
         local capath
-        local python_cmd=${1:-python}
-        capath=$($python_cmd -c $'try:\n from requests import certs\n print (certs.where())\nexcept ImportError: pass')
+        capath=$(python3 -c $'try:\n from requests import certs\n print (certs.where())\nexcept ImportError: pass')
 
         if [[ ! $capath == "" && ! $capath =~ ^/etc/.* && ! -L $capath ]]; then
             if is_fedora; then