Remove unnecessary python-xcbgen and python-jinja2 from build dependencies

[riyad]

I've tried building the last unportable release without python(3)-xcbgen and python(3)-jinja2 packages on Ubuntu focal and it worked. 🙂
Packages are identical (modulo timestamps and .buildinfo) to the build with those packages installed.

May be a first chip at #188 😉

[ghost]

@Eloston this appears to be up your alley since you started the unportable work.

[Eloston]

@riyad Interesting. Do you have those modules provided elsewhere in your Python 2 installation? You can check by trying to import jinja2 and import xcbgen.

[riyad]

I can import those packages with neither python2 nor python3.

$ python2
Python 2.7.18 (default, Aug  4 2020, 11:16:42)
[GCC 9.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import jinja2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named jinja2
>>> import xcbgen
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named xcbgen
>>>

$ python3
Python 3.8.5 (default, Jul 28 2020, 12:59:40)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import jinja2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ModuleNotFoundError: No module named 'jinja2'
>>> import xcbgen
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ModuleNotFoundError: No module named 'xcbgen'
>>>

A build where I tried to remove python-pkg-resources failed with the following error. It also suggest that jinja2 is vendored in ungoogled-chromium-debian/build/src/third_party/jinja2 : it is!

[...]
[20679/43893] ACTION //components/schema_org:generate_schema_org_code(//build/toolchain/linux/unbundle:default)
FAILED: gen/components/schema_org/schema_org_entity_names.h gen/components/schema_org/schema_org_entity_names.cc gen/components/schema_org/schema_org_property_configurations.h gen/components/schema_org/schema_org_property_configurations.cc gen/components/schema_org/schema_org_property_names.h gen/components/schema_org/schema_org_property_names.cc gen/components/schema_org/schema_org_enums.h gen/components/schema_org/schema_org_enums.cc
/usr/bin/python2 ../../components/schema_org/generate_schema_org_code.py --schema-file ../../third_party/schema_org/schema.jsonld --overrides-file ../../third_party/schema_org/overrides.jsonld --name-file gen/components/schema_org/schema_org_name_data.json --output-dir gen/components/schema_org --templates templates/schema_org_entity_names.cc.tmpl templates/schema_org_entity_names.h.tmpl templates/schema_org_enums.cc.tmpl templates/schema_org_enums.h.tmpl templates/schema_org_property_configurations.cc.tmpl templates/schema_org_property_configurations.h.tmpl templates/schema_org_property_names.cc.tmpl templates/schema_org_property_names.h.tmpl
Traceback (most recent call last):
  File "../../components/schema_org/generate_schema_org_code.py", line 22, in <module>
    env = Environment(loader=PackageLoader('generate_schema_org_code', ''))
  File "/build/src/build/src/components/schema_org/../../third_party/jinja2/loaders.py", line 222, in __init__
    from pkg_resources import DefaultProvider, ResourceManager, \
ImportError: No module named pkg_resources
[20680/43893] LINK ./make_top_domain_list_variables
[20681/43893] ACTION //third_party/blink/public/mojom:mojom_platform__generator(//build/toolchain/linux/unbundle:default)
[20682/43893] ACTION //third_party/blink/public/mojom:mojom_core__parser(//build/toolchain/linux/unbundle:default)
ninja: build stopped: subcommand failed.
make[1]: *** [debian/rules:77: override_dh_auto_build-arch] Error 1
make[1]: Leaving directory '/build/src'
make: *** [debian/rules:64: binary] Error 2
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2
Error: error building at STEP "RUN dpkg-buildpackage -b -uc": error while running runtime: exit status 2

I also found xcbgen vendored in ungoogled-chromium-debian/build/src/third_party/xcbproto/src/xcbgen .

[Eloston]

Huh, interesting. I never considered the Python modules to be bundled too. Thanks for investigating!