docs: gdb: do not use incomplete sysroot

That path was from the ARM (or Linaro?) toolchains. We've switched to
the Bootlin ones, and they do not ship this file. There's another one,
`host/arm-buildroot-linux-gnueabihf/sysroot/usr/share/buildroot/gdbinit`,
but it only sets sysroot, and the sysroot it uses only contains the
toolchain's own sysroot. The full command already sets a sysroot with
the `target/` directory, which is sufficient, as it also gets whatever
the toolchain distributes.

Change-Id: I92d590b14e955d70398a8f7af8e9ba3fc98c43bb
diff --git a/doc/architecture.md b/doc/architecture.md
index d7bb9cf..af484df 100644
--- a/doc/architecture.md
+++ b/doc/architecture.md
@@ -101,7 +101,7 @@
 user@laptop ~/build/br-cfb $ make cla-sysrepo-reconfigure
 user@laptop ~/build/br-cfb $ scp per-package/cla-sysrepo/target/usr/bin/cla-sysrepod root@10.10.10.228:/tmp/
 user@laptop ~/build/br-cfb $ ssh root@10.10.10.228 gdbserver :33666 /tmp/cla-sysrepod ...some args here...
-user@laptop ~/build/br-cfb $ ./host/usr/bin/arm-linux-gdb -x staging/usr/share/buildroot/gdbinit \
+user@laptop ~/build/br-cfb $ ./host/usr/bin/arm-linux-gdb \
   per-package/cla-sysrepo/target/usr/bin/cla-sysrepod --ex 'set sysroot target/' \
   --ex 'target remote 10.10.10.228:33666' --ex c
 ```