Remove ConfigLoader and TemplatedConfigLoader

[merelcht]

Description

OmegaConfigLoader will be the config loader from 0.19.0 onwards.

Context

https://github.com/kedro-org/kedro/milestone/34

To do:

• Remove ConfigLoader
• Remove TemplatedConfigLoader
• Remove all other code related to these config loaders
• Remove any docs about these loaders and re-order the OmegaConfigLoader content where needed.
• Can we remove the anyconfig dependency? Double check if any other parts of our codebase are using it.

[astrojuanlu]

A few of places that still use anyconfig:

kedro/kedro/framework/startup.py

Lines 78 to 79 in f89a504

	try:
	metadata_dict = anyconfig.load(pyproject_toml)

kedro/kedro/framework/cli/micropkg.py

Lines 262 to 264 in f89a504

	import anyconfig # for performance reasons
	config_dict = anyconfig.load(metadata.config_file)

kedro/kedro/framework/cli/utils.py

Lines 405 to 406 in f89a504

	if value:
	config = anyconfig.load(value)[section]

[ankatiyar]

Closed with #3253 and #3257