[cleanup] fix .gitignore file and remove files

.gitignore

gtk3-mushrooms/FETCH_HEAD

gtk3-mushrooms/HEAD

gtk3-mushrooms/config

gtk3-mushrooms/description

gtk3-mushrooms/hooks/applypatch-msg.sample

gtk3-mushrooms/hooks/commit-msg.sample

gtk3-mushrooms/hooks/fsmonitor-watchman.sample

gtk3-mushrooms/hooks/post-update.sample

gtk3-mushrooms/hooks/pre-applypatch.sample

gtk3-mushrooms/hooks/pre-commit.sample

gtk3-mushrooms/hooks/pre-push.sample

gtk3-mushrooms/hooks/pre-rebase.sample

gtk3-mushrooms/hooks/pre-receive.sample

gtk3-mushrooms/hooks/prepare-commit-msg.sample

gtk3-mushrooms/hooks/update.sample

gtk3-mushrooms/info/exclude

...ts/pack/pack-f4fd476275936aa1c9beed3d5916136579057be3.idx

...s/pack/pack-f4fd476275936aa1c9beed3d5916136579057be3.pack

gtk3-mushrooms/packed-refs