std.container: RedBlackTree.remove readability enhancement.
fix Issue 12859 - Read-modify-write operation for shared variable in Phobos
Mark some unittest blocks deprecated to suppress messages during Phobos build
Merge pull request #2281 from 9rnsr/fix12859

[REG2.066a] Issue 12859 - Read-modify-write operation for shared variable in Phobos
Merge pull request #2247 from Safety0ff/rbrefac

std.container: RedBlackTree.remove readability enhancement.