MAINTAINERS: Drop Rex Zhu for amdgpu powerplay

No longer works on the driver.
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

MAINTAINERS

@@ -856,7 +856,6 @@ S:	Maintained
 F:	drivers/i2c/busses/i2c-amd-mp2*
 
 AMD POWERPLAY
-M:	Rex Zhu <rex.zhu@amd.com>
 M:	Evan Quan <evan.quan@amd.com>
 L:	amd-gfx@lists.freedesktop.org
 S:	Supported