Patch to remove non-historical EGCS references from libstdc++-v3

[Gabriel Dos Reis]

"Joseph S. Myers" <jsm28@cam.ac.uk> writes:

| The libstdc++-v3 docs are full of non-historical EGCS references.
| This patch cleans them up somewhat.  As a patch to the GCC web pages
| it would probably count as obvious, but I don't know the libstdc++-v3
| procedures; OK to commit?

OK.

-- Gaby
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