Remove srst_pulls_trst from LPC2148 target

srst_pulls_trst is only true on some (broken) LPC2148 boards, a fact
which is already documented in doc/openocd.texi, so it shouldn't be
set unconditionally in the target tcl.

This patch was needed to reflash when an Abort exception occured very
early after reset, before OpenOCD tried to halt the CPU.

tcl/target/lpc2148.cfg

@@ -22,7 +22,7 @@ jtag_ntrst_delay 200
 # JTAG, power-on reset is not enough, i.e. you need to perform a
 # reset before being able to talk to the LPC2148, attach is not possible.
 
-reset_config trst_and_srst srst_pulls_trst
+reset_config trst_and_srst
 
 jtag newtap $_CHIPNAME cpu -irlen 4 -ircapture 0x1 -irmask 0xf -expected-id $_CPUTAPID