[DCK] Remove outdated samples

- `l10n-spain` was never a good sample, since only Spanish projects would have it. Since Tecnativa/doodba#86 it's simply not needed in most cases. Devs can check the docs to know the structure. Thus, it can be removed from here.
- `checksumdir` is not used anymore in `module_auto_update` since OCA/server-tools#1190.
- `xlsxwriter` is included in Odoo 10+.
- `requests` is included in Odoo 8+.

odoo/custom/dependencies/pip.txt

@@ -1,6 +1,3 @@
-checksumdir
 git+https://github.com/OCA/openupgradelib.git@master
 unicodecsv
 unidecode
-requests
-xlsxwriter

odoo/custom/src/repos.yaml

@@ -15,14 +15,3 @@
         - ocb $ODOO_VERSION
         # Example of a merge of the PR with the number <PR>
         # - oca refs/pull/<PR>/head
-
-# Example of an OCA repository
-./l10n-spain:
-    defaults:
-        depth: $DEPTH_DEFAULT
-    remotes:
-        oca: https://github.com/OCA/l10n-spain.git
-    target:
-        oca $ODOO_VERSION
-    merges:
-        - oca $ODOO_VERSION