Remove libgreen support.

[zwarich]

No description provided.

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/3362

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[zwarich]

r? @larsbergstrom

[bors-servo]

saw approval from larsbergstrom
at https://github.com/zwarich/servo/commit/e3b7aeb531b489d136c1d11cf0aea7acdd03b24b

[bors-servo]

merging zwarich/servo/remove-libgreen = e3b7aeb into auto

[bors-servo]

zwarich/servo/remove-libgreen = e3b7aeb merged ok, testing candidate = 92cc423

[bors-servo]

all tests pass:
success: http://build.servo.org/builders/linux1/builds/128
success: http://build.servo.org/builders/linux2/builds/128
success: http://build.servo.org/builders/android/builds/195
success: http://build.servo.org/builders/mac1/builds/345
success: http://build.servo.org/builders/mac2/builds/345

[bors-servo]

fast-forwarding master to auto = 92cc423