formula_cellar_checks: check_non_libraries only for new formulae

[ilovezfs]

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This check is overly opinionated and leads to audit failures no one cares to fix, so let's only run it for new formulae. For example, tcl-tk has failed this audit for years:

$ brew audit tcl-tk
tcl-tk:
  * Non-libraries were installed to "/usr/local/opt/tcl-tk/lib"
    Installing non-libraries to "lib" is discouraged.
    The offending files are:
      /usr/local/opt/tcl-tk/lib/Tk.icns
      /usr/local/opt/tcl-tk/lib/Tk.tiff
Error: 1 problem in 1 formula

[MikeMcQuaid]

Could we make this a --new-formula check?

[MikeMcQuaid]

(NOOOOO is a reasonable response 😆)

[ilovezfs]

@MikeMcQuaid yes, it's always good to have extra reasons to reject new formulae.