docs(csharp): fix stale comment on codeql/csharp-queries dependency (#211)

The comment claimed this dependency was 'Required for Dependencies.ql',
but that stopped being true in commit 8913c63 (Jan 2025), which switched
Dependencies.ql's import from the queries-pack-only 'Telemetry.ExternalApi'
to 'semmle.code.csharp.telemetry.ExternalApi', which ships in codeql/csharp-all.

The dependency is still required, but for a different reason:
suites/csharp-audit.qls and suites/csharp-external-api.qls both pull the
upstream cs/untrusted-data-to-external-api query 'from: codeql/csharp-queries',
which only lives in the queries pack, not csharp-all.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: e78d3f00-2ea0-459b-86a2-91adc0e31c50

Author: felickz

csharp/src/qlpack.yml

@@ -5,5 +5,5 @@ suites: suites
 defaultSuiteFile: suites/csharp.qls
 dependencies:
   codeql/csharp-all: "7.1.0"
-  codeql/csharp-queries: "1.8.0" # Required for Dependencies.ql
+  codeql/csharp-queries: "1.8.0" # Required by suites/csharp-audit.qls and suites/csharp-external-api.qls for upstream cs/untrusted-data-to-external-api
   githubsecuritylab/codeql-csharp-libs: "*"