Removes the CSS variables for .form-control. The problem here is we're reassigning an earlier custom property --bs-body-bg with a new custom property --bs-form-control-bg, but the value of that original one stays computed to the first instance. Only two ways to combat this is to redeclare the variable for dark mode (adds file size), or to remove the extra custom variable. Chose to do the latter as this matches our other form controls.
Fixes #37891 (closed).
Before and after:
