avoid checking in node_modules directories.

[sbc100]

This is somewhat related to #5774, but can be done as an intermediate cleanup step.

We currently have two separate node_modules directories checked-in under emscripten:

./tools/node_modules
./tools/eliminator/node_modules

We also use the top level node_modules directory for installing ws which is only used to the socket tests.

After discussing this with @jgravelle-google and @mathiasbynens I'd like to propose that we switch to using npm to install all this stuff at the top level and remove the checked in versions.

As an initial cleanup I already uploaded: #7536

In order to avoid requiring developers to manually run npm install after cloning (at least initially) I'm proposing to run this transparently from emcc's check_sanity if needs be. A bit like how we build libc on demand behind the scenes.

emsdk users should never have to run npm install since the SDK should alwasy include the correct versions.

[kripken]

Sounds like a noticeable change could be that non-emsdk users would need to install npm (and not just node, although the official downloads contain both)?

[sbc100]

I'm pretty you node always comes with npm... but that it something I will verify and mention on them mailing list.

[stale]

This issue has been automatically marked as stale because there has been no activity in the past year. It will be closed automatically if no further activity occurs in the next 7 days. Feel free to re-open at any time if this issue is still relevant.