Remove deprecated commands

[dbrgn]

Three commands were deprecated in the last release of tealdeer (1.5.0, almost a year ago) and can be removed now:

• --config-path (use --show-paths instead)
• -o / --os (use -p/--platform instead)
• -m / --markdown (use -r/--raw instead)

[dbrgn]

Merging without review, I assume this will not be controversial.