revert docs about cross-platform building

We won't have correct dependencies when parsing the METADATA
files because we need to pass the target platforms there. I
think I got too happy too soon about the possibility of having
correct builds with just 'download_only = True'.

Author: aignas

docs/pypi-dependencies.md

@@ -307,59 +307,6 @@ leg of the dependency manually. For instance by making
 perhaps `apache-airflow-providers-common-sql`.
 
 
-(bazel-downloader)=
-### Multi-platform support
-
-Multi-platform support of cross-building the wheels can be done in two ways - either
-using {bzl:attr}`experimental_index_url` for the {bzl:obj}`pip.parse` bzlmod tag class
-or by using the {bzl:attr}`pip.parse.download_only` setting. In this section we
-are going to outline quickly how one can use the latter option.
-
-Let's say you have 2 requirements files:
-```
-# requirements.linux_x86_64.txt
---platform=manylinux_2_17_x86_64
---python-version=39
---implementation=cp
---abi=cp39
-
-foo==0.0.1 --hash=sha256:deadbeef
-bar==0.0.1 --hash=sha256:deadb00f
-```
-
-```
-# requirements.osx_aarch64.txt contents
---platform=macosx_10_9_arm64
---python-version=39
---implementation=cp
---abi=cp39
-
-foo==0.0.3 --hash=sha256:deadbaaf
-```
-
-With these 2 files your {bzl:obj}`pip.parse` could look like:
-```
-pip.parse(
-    hub_name = "pip",
-    python_version = "3.9",
-    # Tell `pip` to ignore sdists
-    download_only = True,
-    requirements_by_platform = {
-        "requirements.linux_x86_64.txt": "linux_x86_64",
-        "requirements.osx_aarch64.txt": "osx_aarch64",
-    },
-)
-```
-
-With this, the `pip.parse` will create a hub repository that is going to
-support only two platforms - `cp39_osx_aarch64` and `cp39_linux_x86_64` and it
-will only use `wheels` and ignore any sdists that it may find on the PyPI
-compatible indexes.
-
-```{note}
-This is only supported on `bzlmd`.
-```
-
 (bazel-downloader)=
 ### Bazel downloader and multi-platform wheel hub repository.