flask: clean up initialization and #defines

flask: clean up initialization and #defines

This removes the FLASK_DEVELOP and FLASK_BOOTPARAM configuration
parameters which have never been settable by users.  Disabling the
FLASK_DEVELOP configuration option has not produced a compiling
hypervisor for some time, and the FLASK_BOOTPARAM option will be
replaced with a more flexible boot parameter.

This also changes the return type of xsm_initcall_t to void to properly
reflect the fact that the caller ignores the return value.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>