gdb/gdbserver: Remove reference to vec-ipa.o

gdb/gdbserver: Remove reference to vec-ipa.o

This comit:

    commit 0dc327459b19e6765c8fe80957f5c8620611628e
    Date:   Mon Oct 7 16:38:53 2019 +0100

        gdb: Remove vec.{c,h} and update code to not include vec.h

Broke the GDB build due to leaving a reference to vec-ipa.o in the
Makefile.in, this file is built from vec.c which has been removed.

I got away with this as I had an old version of the vec-ipa.o file
still in my build tree.

With this commit in place a clean build now completed successfully.

gdb/ChangeLog:

	* Makefile.in: Remove references to vec-ipa.o.

Change-Id: I4cf55951158dd7ee8f60cd054311a7c367e1d7bf