package/gdb: drop not needed dependencies

Signed-off-by: Phil Sutter <phil@nwl.cc>

package/gdb/Makefile

@@ -7,7 +7,7 @@ include ${ADK_TOPDIR}/toolchain/gdb/Makefile.inc
 PKG_NAME:=		gdb
 PKG_DESCR:=		programm debugger
 PKG_SECTION:=		app/debug
-PKG_DEPENDS:=		libthread-db libncurses libexpat zlib
+PKG_DEPENDS:=		libncurses zlib
 PKG_BUILDDEP:=		ncurses readline expat zlib
 PKG_NOPARALLEL:=	1