🏗 Remove bundlesize from package.json

[rsimha]

We use the bundlesize package to compute the size of the AMP runtime during PR checks. This is done here:

amphtml/build-system/tasks/bundle-size.js

Lines 46 to 49 in ebe9247

	function getGzippedBundleSize() {
	const cmd = `npx bundlesize -f "${runtimeFile}"`;
	log('Running', cyan(cmd) + '...');
	const output = getStdout(cmd).trim();

It turns out that bundlesize uses the iltorb library, which on Mac, requires Xcode to be installed on the device.

Since calls to npx foo don't need foo to be listed in package.json, we can remove bundlesize from package.json. This should mitigate the requirement of Xcode on mac laptops and make initial setup easier.

Fixes #19048
Closes #20775

[rsimha]

/to @danielrozenberg @alabiaga @jonkeller

[rsimha]

Bundle size check on Travis looks good: https://travis-ci.org/ampproject/amphtml/jobs/491814430#L673-L679

Merging this after green build appears.

[danielrozenberg]

And this works locally too? Sorcery!