test: do not drop SQL_BUILTIN functions

SQL_BUILTIN was introduced in [1] (tarantool 2.2.1) and dropped in [2]
(tarantool 2.10.0-beta2). It is not permitted to drop SQL_BUILTIN
functions, thus, before this patch, tarantool_python_ci.lua was unable
to run with versions between 2.2.1 and 2.10.0-beta2, failing with
`ER_DROP_FUNCTION: Can't drop function 1: function is SQL built-in`.
This patch fixes this.

tarantool_python_ci.lua is used to start a tarantool instance for
Windows tests.

1. tarantool/tarantool@200a492
2. tarantool/tarantool@c49eab9

Part of #182

Author: DifferentialOrange

test/suites/lib/tarantool_python_ci.lua

@@ -179,16 +179,23 @@ clean = function()
     end)
 
     local _FUNC_NAME = 3
+    local _FUNC_LANGUAGE = 5
     local allowed_funcs = {
         ['box.schema.user.info'] = true,
     }
+    local allowed_langs = {
+        ['SQL_BUILTIN'] = true,
+    }
     box.space._func:pairs():map(function(tuple)
         local name = tuple[_FUNC_NAME]
-        return name
-    end):filter(function(name)
-        return not allowed_funcs[name]
-    end):each(function(name)
-        box.schema.func.drop(name)
+        local lang = tuple[_FUNC_LANGUAGE]
+        return { name = name, lang = lang }
+    end):filter(function(prop)
+        return not allowed_funcs[prop.name]
+    end):filter(function(prop)
+        return not allowed_langs[prop.lang]
+    end):each(function(prop)
+        box.schema.func.drop(prop.name)
     end)
 
     cleanup_cluster()