Consider dropping protection against line-height introduced in #23104

#23104 (closed) was about a way to discover the Tor Browser platform by checking the computed line-height.

However, with Bug 1536871, Mozilla added an alternative protection, that makes getComputedStyle return normal, instead of the real pixel value.

Therefore, we should consider that fix deprecated, and remove it from our patch set.

Here is the test of the patch, quickly modified to display the value to the user.

Please notice its current result:

which is coherent with Firefox and with Chromium-based browsers.