Revision 510679

devel/spdlog: Use system fmt

This is in preparation for updating devel/libfmt to 6.0.0.  Spdlog
bundles fmt 5.3.0 which is incompatible with 6.0.0.  This would
lead to problems in consumers that use both.

PR:		240148
Submitted by:	jbeich
Approved by:	vanilla (maintainer)