Revert "Create a .gitignore file in the CANONICAL_O directory"

The packages 'python-jsonschema-specifications', 'pydantic-core', and
likely other packages based on Python maturin silently stopped
installing files to the host and target directories after commit
a14c862c08.

A similar issue was reported by the Conda project[1]. It seems some
build tools scan for gitignore files to decide what files to build
and install.

I attempted various combinations of gitignore patterns including
mimicking the Conda project's gitignore[2], but the only thing that has
worked reliably is the original `/output` ignore in the root Buildroot
directory.

This reverts commit a14c862c08.

[1] https://github.com/PyO3/maturin/issues/1911
[2] https://github.com/conda-forge/conda-smithy/blob/main/conda_smithy/feedstock_content/.gitignore
Reported-by: Bryan Brattlof <bb@ti.com>
Signed-off-by: Brandon Maier <brandon.maier@collins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

.gitignore

@@ -1,3 +1,4 @@
+/output
 /dl
 /.auto.deps
 /.config.cmd

Makefile

@@ -63,9 +63,6 @@ ifneq ($(findstring @,$(CANONICAL_O)),)
 $(error The build directory can not contain a '@')
 endif
 
-# Create a default .gitignore file that ignores everything
-$(shell echo "*" > "$(CANONICAL_O)/.gitignore")
-
 CANONICAL_CURDIR = $(realpath $(CURDIR))
 
 REQ_UMASK = 0022