Remove Krasi as TSDB maintainer
* `prometheus-mixin`: @beorn7
* `storage`
* `remote`: @csmarchbanks, @cstyan, @bwplotka
-* `tsdb`: @codesome, @krasi-georgiev, @bwplotka
+* `tsdb`: @codesome, @bwplotka
* `web`
* `ui`: @juliusv
* `Makefile` and related build configuration: @simonpasquier, @SuperQ
