btrfs-progs: ci: temporarily disable gitlab CI

The jobs has been failing for some time due the time limit 1h:

+ qemu-system-x86_64 -m 512 -nographic -kernel /repo/bzImage -drive
  file=/repo/qemu-image.img,index=0,media=disk,format=raw -fsdev
  local,id=btrfs-progs,path=/repo,security_model=mapped -device
  virtio-9p-pci,fsdev=btrfs-progs,mount_tag=btrfs-progs -append
  'console=tty1 root=/dev/sda rw'
  main-loop: WARNING: I/O thread spun for 1000 iterations
  ERROR: Job failed: execution took longer than 1h0m0s seconds

We'd still like to use the qemu test as it could pull the recent
development kernel that the base image does not provide. However the
overall performance is too bad and it does not make sense to waste
GitLab resources.

Also remove the build status badge from README as it changed at some
point and does not render as a SVG image anymore.

Issue: #171
Signed-off-by: David Sterba <dsterba@suse.com>

README.md

@@ -1,4 +1,4 @@
-Btrfs-progs [![build status](https://travis-ci.org/kdave/btrfs-progs.svg?branch=devel)](https://travis-ci.org/kdave/btrfs-progs) [![coverity status](https://scan.coverity.com/projects/617/badge.svg)](https://scan.coverity.com/projects/btrfs-progs) [![gitlab CI/CD](https://gitlab.com/kdave/btrfs-progs)](https://gitlab.com/kdave/btrfs-progs/badges/devel/build.svg)
+Btrfs-progs [![build status](https://travis-ci.org/kdave/btrfs-progs.svg?branch=devel)](https://travis-ci.org/kdave/btrfs-progs) [![coverity status](https://scan.coverity.com/projects/617/badge.svg)](https://scan.coverity.com/projects/btrfs-progs)
 ===========
 
 Userspace utilities to manage btrfs filesystems.