tools: configure --with-intl=full-icu warns 3x

[srl295]

Just the place for a Snark! I have said it thrice. What I tell you three times is true. —L. Carroll

• Version: master 01a1296
• Platform: Mac
• Subsystem: tools

$ ./configure --with-intl=full-icu
Warning: Not downloading package "icu". You could pass "--download=all"
    (Windows: "download-all") to try auto-downloading it.
Warning: Not downloading package "icu". You could pass "--download=all"
    (Windows: "download-all") to try auto-downloading it.
Warning: Not downloading package "icu". You could pass "--download=all"
    (Windows: "download-all") to try auto-downloading it.
WARNING: * ECMA-402 (Intl) support didn't find ICU in deps/icu..
ERROR: Cannot build Intl without ICU in deps/icu.
       Fix, or disable with "--with-intl=none"

One exactly duplicate warning would suffice.

[refack]

Might be resolved by #26725

[srl295]

@refack at least, i won't try to fix it until that lands! thanks.

[richardlau]

Proposed fix: #27031