libcore: Remove `extern mod { ... }` from libcore. rs=deexterning
libstd: Remove `extern mod { ... }` from libstd. rs=deexterning
librustc: Remove "extern mod { ... }" from librustc, librustdoc, and tests. rs=deexterning
libsyntax: Stop parsing structural record types
librustc: Remove structural record types from the compiler
libsyntax: Remove struct literal expressions from the compiler
librustc: Remove record patterns from the compiler
auto merge of #5249 : pcwalton/rust/extern-mod-records, r=brson

r? @brson