DEVELOPERS: drop Mathieu Audat

Mathieu privately informed me that he no longer has access to the
TS4900 board, he is therefore unable to maintain this board moving
forward. Let's drop his entry from the DEVELOPERS file.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

DEVELOPERS

@@ -2215,11 +2215,6 @@ N:	Masahiro Yamada <yamada.masahiro@socionext.com>
 F:	board/arm/foundation-v8/
 F:	configs/arm_foundationv8_defconfig
 
-N:	Mathieu Audat <mathieuaudat@gmail.com>
-F:	board/technologic/ts4900/
-F:	configs/ts4900_defconfig
-F:	package/ts4900-fpga/
-
 N:	Matt Silva <dev@matt-silva.com>
 F:	package/rlwrap/