Remove note on no-support for Windows system certificate store

What does this MR do?

Remove the note on no-support for Windows system certificate store.
As the issue that was pointed from here (crypto/x509: make SystemCertPool work on Windows? #16736) seems to have been resolved by below commit.
crypto/x509: verification with system and custom roots (Notice Fixes #16736)

Actually my own Windows runner has successfully been accessing my GitLab instance under its certificate signed by a custom CA certificate installed in the Windows certificate store.

A bit of background

One of our customers inquired us (a GitLab channel & PS partner) with confusion that one of their runners works and the other does not with the same configuration except for the system certificate store.

Related issues

n/a

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