Resolve expi() documentation issues due to deprecation.

[veelo]

Fix issue 19733: https://issues.dlang.org/show_bug.cgi?id=19733

Nowadays, the x87 instruction fsincos is slower, not faster, than computing sin and cos separately.
https://stackoverflow.com/questions/12485190/calling-fsincos-instruction-in-llvm-slower-than-calling-libc-sin-cos-functions
Therefore, there is no need for assembly in the expi() implementation, which was removed in commit 029440c.

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[thewilsonator]

Please amend the commit message to say "Fix issue 19733: ..." so the bot picks it up.

[veelo]

Please amend the commit message to say "Fix issue 19733: ..." so the bot picks it up.

Will try.

[kinke]

As stated in bugzilla, I saw a significant boost (~5x faster) with the x87 asm version with LDC on my i5-3550. The linked StackOverflow question isn't related to 80-bit real at all.

[veelo]

@kyllingstad For what reasons was the x87 asm version removed from std.complex.expi? 029440c

[kyllingstad]

@kyllingstad For what reasons was the x87 asm version removed from std.complex.expi? 029440c

See discussion in PR #559, in particular Don's comment

[ghost]

Just noticed this - I wrote a similar PR yesterday, which is meanwhile merged. Hence, this PR can be closed. ("Having Fix - issue 19733 [...]" in the commit message would have maked the bot adding a link to this PR in bugzilla and I would have known of it earlier.)