update beamer-slimmer

%% Cell type:code id: tags:

``` python

from pdfrw import PdfReader, PdfWriter

def run_stage(src, out):

  i = PdfReader(src)

  o = PdfWriter()

  sum_i = len(i.pages)

  num_i = i.Root.PageLabels.Nums

  for r in range(1, len(num_i) // 2):

    o.addpage(i.pages[int(num_i[r * 2]) - 1])

  o.addpage(i.pages[sum_i - 1])

  o.write(out)

run_stage("slides.pdf", "res.pdf")

```

%% Cell type:code id: tags:

``` python

run_stage("open.pdf", "res.pdf")

```