remote.h: retire CAS_OPT_NAME

remote.h: retire CAS_OPT_NAME

When the "--force-with-lease" option was introduced in 28f5d176
(remote.c: add command line option parser for "--force-with-lease",
2013-07-08), the design discussion revolved around the concept of
"compare-and-swap", and it can still be seen in the name used for
variables and helper functions.  The end-user facing option name
ended up to be a bit different, so during the development iteration
of the feature, we used this C preprocessor macro to make it easier
to rename it later.

All of that happened more than 10 years ago, and the flexibility
afforded by the CAS_OPT_NAME macro outlived its usefulness.  Inline
the constant string for the option name, like all other option names
in the code.

Signed-off-by: Junio C Hamano <gitster@pobox.com>