Remove preprocess hook for filename and file size that's now provided in localgov_core

LocalGov Base 2.4.0 and 1.10.1 removes a preprocess hook to format file name and file size that is now included in LocalGov Core.

We prefer not to force LocalGov Base to depend on any version of LocalGov Core so to keep the preprocess, maintainers should run LocalGov Core versions 2.16.0 (Drupal 10) and 3.1.0 (for Drupal 11) and above.