Remove libexpat.la to avoid linker issues after upgrading libexpat to 2.7.1

When libexpat is upgraded from version 2.2.5 to 2.7.1, the generated libexpat.la
file may inject unnecessary linker flags during the GDB build process. This can
introduce unnecessary dependencies like -lm and the libm.a static archive,
leading to link errors in environments where such libraries are not available.

Deleting libexpat.la ensures a cleaner and more reliable link process.

Change-Id: Ib36046556ef71badea284bfead47fac06ad67efe
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/c/dsg-gnu/Internal/gnu-devtools-for-arm/+/768420


Reviewed-by: Vaseeharan Vinayagamoorthy <vaseeharan.vinayagamoorthy@arm.com>
Tested-by: Service account - used by users in DSG GNU team <dgboter@arm.com>