refactor(init): integration_default

[mrtnvgr]

No description provided.

[rewhile]

integration_default is causing way too much maintenance burden:

• fix(integration_default): override enabled key only if integration has one #559 Implemented inside setup function, doesn't leverage feat(integrations): accept both boolean and table config #534

• feat(barbecue): add enabled key #560 This is a monkeypatch used only for bufferline because of a past mistake. I do not encourage patching the .get() function.

• refactor(init): integration_default #562 integration_default = true is currently useless because all are already enabled by default (Except navic which should have been true by default)

• Currently, the only use for this is to disable all integrations by default

With the above points, I think it's best we remove this feature for now because the current solution is suboptimal. If people really want this feature it's best that we implement it inside the compiler.