Remove unused .fakeroot.* mechanism

There used to be a mechanism using which packages could leave a
.fakeroot.<something> file which could contain commands to be executed
within the fakeroot environment. Since this mechanism is no longer
used by any package, remove it from the common infrastructure.

The latest user was nfs-utils, which used this mechanism to do the
"make install" as root, since doing otherwise was not supported. But
since 16e7b825, nfs-utils has been
upgraded and converted to the package infrastructure, and this hack is
no longer necessary. Another past user was the ltp-testsuite package,
for the same reason, and since
a72a6704, the fakeroot hack is no
longer needed.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>