Use .deb libtool instead of savannah version

This is to avoid the downloading problems we are having
from the Savannah git repo from GNU.

snapcraft.yaml

@@ -72,17 +72,13 @@ parts:
  - python3-pip
 
  libtool:
- source: https://git.savannah.gnu.org/git/libtool.git
- source-tag: 'v2.4.7'
- plugin: autotools
+ plugin: nil
 # ext:updatesnap
 # version-format:
 # ignore: true
- autotools-configure-parameters: [ --prefix=/usr ]
- build-environment: *buildenv
- build-packages:
- - help2man
- - texinfo
+ stage-packages:
+ - libtool
+ - libtool-bin
  override-stage: |
  set -eux
  craftctl default
@@ -857,6 +853,7 @@ parts:
  - libtdb-dev
  - libpulse-dev
  - libgstreamer1.0-dev
+ - libltdl-dev
 
  gsound:
  after: [ libcanberra, meson-deps ]
@@ -1399,6 +1396,7 @@ parts:
  - libjpeg-dev
  - libkrb5-3
  - liblcms2-dev
+ - libltdl-dev
  - liblzo2-dev
  - liblzo2-2
  - liblzma5