Revert converting decimal image sizes to integers for sizer SVG generation

[schlessera]

Feature description

For the issue with decimal image sizes described at #4493, we resorted to a workaround while the validator was being adapted, by truncating the image sizes to integer values for the SVG generation.

As ampproject/amphtml#27528 has been fixed upstream, we should revert this work-around.

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Acceptance criteria

• Decimal sizes are used as-is for sizer generation.

Implementation brief

• Remove code & tests introduced by Image with decimal dimensions causes Optimizer to emit AMP Validation error  #4493

QA testing instructions

Demo

Changelog entry

[johnwatkins0]

Moving this to QA Passed now, as I was able to add an AMP image with a decimal dimension locally, and no validation errors appeared.