resourceloader: Remove ESI support (previously disabled)

resourceloader: Remove ESI support (previously disabled)

These were never enabled or used in production and are not
compatible with the upcoming async changes (T107399). To avoid
having to maintain compatibility with this, remove it for now.

The current on-going request to operations for ESI support is unrelated
to this code.

Considered making makeResourceLoaderLink() protected as it's not
used anywhere in @wikimedia Git outside mediawiki-core. And the unit
test actually treated it as protected already. However it's called
in SpecialJavaScriptTest so leaving that as-is for now.

In Icba6d7a87b239 the signature will change again with the removal
of the $loadCall parameter, which is obsolete in an async world
due to document.write being forbidden.

Change-Id: I9f557cc794638ffd15329934865e21e1027f7cfa