nios2: Sync GDB version with other toolchain builds

For some reason nios2 had selected GDB 7.12.1.  Use the latest gdb to
be in sync with what is used for all the other toolchains.

Signed-off-by: Kumar Gala <[email protected]>

Author: galak

configs/nios2.config

@@ -20,7 +20,6 @@ CT_LIBC_NEWLIB_NANO_FORMATTED_IO=y
 CT_CC_GCC_EXTRA_CONFIG_ARRAY="--with-gnu-ld --with-gnu-as"
 CT_CC_LANG_CXX=y
 CT_DEBUG_GDB=y
-CT_GDB_V_7_12_1=y
 CT_ISL_V_0_18=y
 CT_LIBICONV_NEEDED=y
 # CT_COMP_TOOLS_AUTOCONF is not set