build: Cleanup depends build system

Summary:

build: Drop non-existent share/pkgconfig directory

build: Remove unneeded share/doc directory from expat package

build: Remove empty var/cache/fontconfig directory from fontconfig

build: Remove unneeded share/man directory from freetype package

build: Remove unneeded share/man directory from libXau package

This is a backport of core#22783

Depends on D13872

Test Plan:
gitian builds

contrib/guix/guix-build

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13873