mpy-cross,unix: Remove .gitignore file.

Now that all build artefacts are placed in a build/ directory the gitignore
is no longer needed.

Signed-off-by: Damien George <damien@micropython.org>

mpy-cross/.gitignore

@@ -1 +0,0 @@
-mpy-cross

ports/unix/.gitignore

@@ -1,3 +0,0 @@
-micropython
-micropython-*
-*.gcov