shell: Handle '--emulate-fhs' in 'guix shell', not in 'guix environment'.

shell: Handle '--emulate-fhs' in 'guix shell', not in 'guix environment'.

Previously, using 'guix shell -CF coreutils' twice (such that the
profile is cache) would result in:

  guix shell: error: '--profile' cannot be used with package options

This patch fixes it by moving argument handling to (guix scripts shell),
before 'options-with-caching' is called.

* guix/scripts/environment.scm (show-environment-options-help)
(%options): Remove '--emulate-fhs'.
(guix-environment*): Pass OPTS as-is to 'options/resolve-packages'.
* guix/scripts/shell.scm (show-help, %options): Add '--emulate-fhs'.
Add the (expression . ...) component to RESULT right from the argument
handler.
* tests/guix-environment-container.sh: Change '--emulate-fhs' tests to
use 'guix shell' instead of 'guix environment'.