Fix sampler scheduler autocorrection warning

[w-e-w]

Description

fix unnecessary sampler scheduler autocorrection warning

• caused by more old sampler scheduler compatibility #15681

from Discussions post

• Sampler Scheduler autocorrection??? #16053

user has reported erroneous scheduler autocorrection warning

essentially under certain circumstances such as
sampler DPM++ 2M + schedule Karras they will see the sampler scheduler autocorrection warning

this is because of default schedule for DPM++ 2M is Karras, and so the retruned schedule of get_sampler_and_scheduler() will be Automatic Karras
this triggers a false warning because Automatic != Karras

functionality wise It's harmless but it does confuse people

fix:
add new a arg convert_automatic: boolto get_sampler_and_scheduler() that disables revert back to Automatic if it's the default scheduler for the selected sampler behavior

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additional unrelated change that I decide to throw in

• in multi size grid #15988 I forgot to remove one line of comment

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests

[BurnZeZ]

Yeah, it makes it seem like it’s switching to a different scheduler.