Revert "Fixed #23935 -- Convert decimals to fixed point for display in django admin"

This reverts commit 9e325ff0647e87820ba4b82a7f68f77fdd5d8ace.
Revert "regression unit tests for Decimal in display_for_field"

This reverts commit 454827e863a9914532cd6c68b22789ee755c9325.
Fixed utils/numberformat.format for Decimal outputing scientific notation