Remove some redundant animation interpolation code

[upsuper]

This change is 

[highfive]

Heads up! This PR modifies the following files:

• @bholley: components/style/properties/helpers/animated_properties.mako.rs
• @emilio: components/style/properties/helpers/animated_properties.mako.rs

[upsuper]

Not sure who should review this... probably @hiikezoe or @birtles

[upsuper]

r? @hiikezoe

[upsuper]

@bors-servo try

[bors-servo]

⌛ Trying commit 61eb7e0 with merge ef028be12a301257d01e22d5328ce80eb8c52f00...

[hiikezoe]

Reviewed 1 of 1 files at r1.
Review status: 0 of 2 files reviewed at latest revision, 1 unresolved discussion.

---

components/style/properties/helpers/animated_properties.mako.rs, line 365 at r2 (raw file):

% if not prop.is_animatable_with_computed_value:
                        let value: longhands::${prop.ident}::computed_value::T = value.into();
                    % endif

What I couldn't find initially was that the corresponding part of this change for stylo. Yeah, it's done in the first commit. Rust trait magic. Great!

---

Comments from Reviewable

[hiikezoe]

Awesome! Thank you Xidorn!
r=me with a try for stylo.

[upsuper]

Let's see https://treeherder.mozilla.org/#/jobs?repo=try&revision=c3da17bd9bbd1606ec1c2ec5722ba05e712efdb7

[bors-servo]

💔 Test failed - linux-rel-wpt

[upsuper]

@bors-servo retry

[bors-servo]

⌛ Trying commit 61eb7e0 with merge 67eaae8...

[bors-servo]

💔 Test failed - linux-rel-wpt

[upsuper]

Stylo try run looks good so far. There are three different intermittents appear on Servo try run. Based on the content of the tests, I believe they are unrelated to changes here. FWIW:

• http://build.servo.org/builders/linux-rel-wpt/builds/4433/steps/shell__2/logs/filtered-wpt-errorsummary.log
• http://build.servo.org/builders/linux-rel-css/builds/4414/steps/shell__2/logs/filtered-css-errorsummary.log
• http://build.servo.org/builders/linux-rel-wpt/builds/4434/steps/shell__2/logs/filtered-wpt-errorsummary.log

[upsuper]

@bors-servo r=hiikezoe

[bors-servo]

📌 Commit 61eb7e0 has been approved by hiikezoe

[bors-servo]

⚡ Previous build results for android, arm32, arm64, linux-dev, linux-rel-css, mac-dev-unit, mac-rel-css1, mac-rel-wpt1, mac-rel-wpt4, windows-msvc-dev are reusable. Rebuilding only linux-rel-wpt, mac-rel-css2, mac-rel-wpt2, mac-rel-wpt3...

[bors-servo]

☀️ Test successful - android, arm32, arm64, linux-dev, linux-rel-css, linux-rel-wpt, mac-dev-unit, mac-rel-css1, mac-rel-css2, mac-rel-wpt1, mac-rel-wpt2, mac-rel-wpt3, mac-rel-wpt4, windows-msvc-dev
Approved by: hiikezoe
Pushing 67eaae8 to master...