replace load_fsdp_monolith_ with load_monolith_

[milocress]

What does this PR do?

Replace load_fsdp_monolith_ with load_monolith_

What issue(s) does this change relate to?

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[mvpatel2000]

LGTM. This is technically BC breaking, but we dont think anyone is using this attribute on state -- it is primarily used internally in Composer. It will avoid making easy mistakes by having two variables with the same name and fixes tests.

We can preserve the old attribute on state and fwd it with a deprecation warning

[mvpatel2000]

LGTM!