install: remove unused `trim()` function
jshintrc: set "es5" mode to true

So that I can use reserved words as property names...
node-gyp: fix lint
install: remove "legacy" installation logic

Now that v0.8.x of node.js is the minimum supported version of node-gyp,
this legacy logic is no longer releavant.
legacy: remove "legacy" dir

No longer used since node v0.8.x is the minimum supported node-gyp version
v0.10.2