Replace the obsolete no-dependencies rationale in every chart helper

The doc comments on the resources and defaultedDict helpers justified the
copy-per-chart with "charts in this repo deliberately have no dependencies".
That rule fell with #214: a dependency is admissible now, just expensive, and
it sits in the README as guideline 14, not 13. The justification still holds,
but its reason is a different one - sharing the helper would mean a library
chart, a second artefact to publish, version and pull for something that
changes about once a year. searxng got that wording in PR #38; this carries it
to 21 further charts, 40 occurrences in all.

rss-bridge is deliberately left out. Its install-test fails on the Gitea
runner for a reason that predates this branch, and touching the chart would
keep it in the install-test matrix and the check red. Its copy of the sentence
is carried by #51, which has to open the chart anyway.

Comments only: every touched chart renders byte-identical against its
ci/<chart>/test-values.yaml. Each published chart takes a patch bump,
appVersion and +up suffix untouched; template-chart is never published and
takes none, but is corrected because every new chart inherits from it.

Two repo files carried the same claim at no version cost:
validate-charts.yml explained the all-charts quantity render test with it, and
change-app-version.yml still counted nine images for freesailarr - MediathekArr
made it ten.

matrix-synapse/templates/_helpers.tpl

@@ -19,9 +19,11 @@ Usage (the values path to the resources dict varies per chart):
   resources:
     {{- include "matrix-synapse.resources" .Values.<app>.resources | nindent 12 }}
 
-NOTE: charts in this repo deliberately have no dependencies, so this helper is
-duplicated into every chart's templates/_helpers.tpl with the chart's name as
-define prefix. This file in template-chart is the reference implementation.
+NOTE: this helper is duplicated into every chart's templates/_helpers.tpl with
+the chart's name as define prefix, because sharing it would mean a library
+chart, and a dependency is admissible but expensive (README, guideline 14) -
+this chart takes none. This file in template-chart is the reference
+implementation.
 */}}
 {{- define "matrix-synapse.resources" -}}
 {{- $resources := . | default dict -}}
@@ -168,8 +170,9 @@ Rules:
   - keys only present in the override are passed through unchanged.
 
 NOTE: like the helpers above, this is duplicated into every chart's
-templates/_helpers.tpl with the chart's name as define prefix, because charts
-in this repo deliberately have no dependencies.
+templates/_helpers.tpl with the chart's name as define prefix, because sharing
+it would mean a library chart and this chart takes no dependency (README,
+guideline 14).
 */}}
 {{- define "matrix-synapse.defaultedDict" -}}
 {{- $defaults := .defaults | default dict -}}