connpool: move source code file

The source files for built-in Lua modules are generally placed on the
same level: in `src/lua` or in `src/box/lua`, disregarding whether
they're public or internal.

The recently introduced `experimental.connpool` built-in module is
placed in the `experimental` subdirectory.

This commit moves `src/box/lua/experimental/connpool.lua` to
`src/box/lua/connpool.lua` to follow the existing file structure.
Public, internal and experimental modules are all on the same level now.

The `connpool` module is still experimental and
`require('experimental.connpool')` is needed to use it.

This commit doesn't change the code of the module.

NO_DOC=no code changes
NO_CHANGELOG=see NO_DOC
NO_TEST=see NO_DOC

src/box/CMakeLists.txt

@@ -76,7 +76,7 @@ if (ENABLE_CONFIG_EXTRAS)
 endif()
 # }}} config
 
-lua_source(lua_sources lua/experimental/connpool.lua      experimental_connpool_lua)
+lua_source(lua_sources lua/connpool.lua connpool_lua)
 
 if (ENABLE_FAILOVER)
     lua_multi_source(lua_sources ${FAILOVER_LUA_SOURCES})

src/box/lua/init.c

@@ -179,7 +179,7 @@ extern char session_lua[],
 #endif
 	/* }}} config */
 
-	experimental_connpool_lua[];
+	connpool_lua[];
 
 /**
  * List of box's built-in modules written using Lua.
@@ -455,9 +455,9 @@ static const char *lua_sources[] = {
 
 	/* }}} config */
 
-	"experimental/connpool",
+	"connpool",
 	"experimental.connpool",
-	experimental_connpool_lua,
+	connpool_lua,
 
 	FAILOVER_LUA_MODULES