Remove bcsnowdata from Suggests; data-raw deps stay outside DESCRIPTION

The pkgdown CI on the squash-merge of #55 failed because bcsnowdata
is GitHub-only (bcgov/bcsnowdata) and pak couldn't resolve it from
CRAN/PPM. Convention in this repo (matching how bcdata and fresh are
already handled in other data-raw scripts) is that data-raw scripts
manage their own ad-hoc deps; the developer running the script installs
what's needed. data-raw/qa_snow_validation.R header now includes the
pak::pak() install instruction.

Author: NewGraphEnvironment

DESCRIPTION

@@ -23,7 +23,6 @@ Roxygen: list(markdown = TRUE)
 RoxygenNote: 7.3.3
 Suggests:
     aws.s3,
-    bcsnowdata,
     bookdown,
     ecmwfr,
     ggplot2,

data-raw/qa_snow_validation.R

@@ -17,7 +17,10 @@
 # Filed against #48 Phase 3.
 #
 # Prerequisites:
-#   - bcgov/bcsnowdata (in DESCRIPTION Suggests)
+#   - bcgov/bcsnowdata installed locally (not in DESCRIPTION; data-raw
+#     scripts manage their own deps per the cd convention). Install with:
+#       pak::pak("bcgov/bcsnowdata")
+#     (also requires `reshape` as a transitive dep)
 #   - cd package installed (or devtools::load_all())
 #   - Network access for ASWS / manual data + S3 reads
 #