action.yml: drop the flavor: full-only caveat on ucrt64

When the `ucrt64` axis first landed, only `flavor: full` worked: the
subset flavors call out to `please.sh create-sdk-artifact` in
`build-extra`, and that script did not understand
`--architecture=ucrt64` at the time. That has since been fixed, so
all four flavors work for `ucrt64`.

Drop the now-stale "only the `full` flavor is supported" sentence
from the action description.

Assisted-by: Opus 4.7
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

action.yml

@@ -18,7 +18,6 @@ inputs:
       MINGW64-to-UCRT64 migration is in progress it is cloned from a
       transitional "ucrt64" branch that will eventually replace "main",
       at which point "x86_64" itself will materialise a UCRT64 SDK.
-      Only the "full" flavor is supported on the "ucrt64" axis for now.
     default: 'x86_64'
   msys:
     required: false