remove obsolete reset_mode

src/target/target/at91r40008.cfg

src/target/target/at91sam9260.cfg

src/target/target/at91sam9260minimal.cfg

src/target/target/eir-sam7se512.cfg

src/target/target/epc9301.cfg

src/target/target/hammer.cfg

src/target/target/ipx42x.cfg

src/target/target/lm3s6965.cfg

src/target/target/lm3s811.cfg

src/target/target/lpc2129.cfg

src/target/target/lpc2148.cfg

src/target/target/lpc2294.cfg

src/target/target/mx31.cfg

src/target/target/netx500.cfg

src/target/target/nslu2.cfg

src/target/target/omap5912.cfg

src/target/target/pxa255.cfg

src/target/target/pxa270.cfg

src/target/target/sam7s256.cfg

src/target/target/sam7x256.cfg