od: gcw0: Disable Valgrind

It takes ages to build, and is somewhat replaced now with GCC's address
sanitizer: https://github.com/google/sanitizers/wiki/AddressSanitizer

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

configs/od_gcw0_defconfig

@@ -66,7 +66,6 @@ BR2_PACKAGE_MEMSTAT=y
 BR2_PACKAGE_PV=y
 BR2_PACKAGE_STRACE=y
 BR2_PACKAGE_STRESS=y
-BR2_PACKAGE_VALGRIND=y
 BR2_PACKAGE_BINUTILS=y
 BR2_PACKAGE_SED=y
 BR2_PACKAGE_DOSFSTOOLS=y