Update layer pins for 2020-07-01

meta-ros as of 2020-06-30 18:17:08 -0700

1a388c06 milestone.conf: Complete Milestone 6
ff648a09 README.md: State what can be built from this branch
d7217ebb ros2_image.bbclass: Add ros2_image_rm_vendor_lib_symlinks()
25c1287c {dashing} rmw-implementation.inc: Remove "rmw-opensplice-cpp" from other ROS_*_DEPENDS
7b27e087 {dashing} Add ros-environment-2.3.0-1.inc
daf8e336 {dashing} Add launch-testing-ros.inc
1dbcf65e {dashing} apriltag.inc: Inherit ros-insane
84029785 {dashing} fastrtps.inc: Inherit ros-insane
422b03a0 {dashing} packagegroup-ros-world-dashing.inc: Drop "teleop-twist-joy" until patched to compile with g++ 8
63e6beef {dashing} packagegroup-ros-world-dashing.inc: Drop "ros-mrpt" DISTRO_FEATURES (MRPT not part of dashing)
daf8d77f {dashing} packagegroup-ros-world-dashing.inc: Drop "launch-testing-ament-cmake" until able to launch qemu
a7244335 {dashing} packagegroup-ros-world-dashing.inc: Drop rem...