disable mail for swarren

I haven't been involved in U-Boot development for quite a while, so
CCing me on patches isn't currently useful. Add a .mailmap entry that I
believe will turn off patch CCs. This can always be removed if I become
active again! Remove myself from a few MAINTAINERS failed and the git
mailrc file too.
diff --git a/doc/git-mailrc b/doc/git-mailrc
index 6214dae..50f896d 100644
--- a/doc/git-mailrc
+++ b/doc/git-mailrc
@@ -74,7 +74,7 @@
 alias snapdragon     uboot, mateusz
 alias socfpga        uboot, marex, dinh, simongoldschmidt, tienfong
 alias sunxi          uboot, jagan, apritzel
-alias tegra          uboot, sjg, Tom Warren <twarren@nvidia.com>, Stephen Warren <swarren@nvidia.com>
+alias tegra          uboot, sjg, Tom Warren <twarren@nvidia.com>
 alias tegra2         tegra
 alias ti             uboot, trini
 alias uniphier       uboot, masahiro