Revert "Set User-Agent for proper activity log sources in Customer.io"

[mike-engel]

Reverts #93

With #93 I introduced a bug where loading the package would immediately cause an unhandled error because of how the typescript files are compiled and published. It naively believes package.json will be in the parent folder, but it's not when build and published.

I'll fix this in a follow up PR with a more robust solution, but this will prevent more crashes when published.

Uncaught:
Error: ENOENT: no such file or directory, open '/home/mike/node_modules/customerio-node/dist/package.json'
    at Object.openSync (fs.js:462:3)
    at Object.readFileSync (fs.js:364:35)
    at Object.<anonymous> (/home/mike/node_modules/customerio-node/dist/lib/request.js:12:35)
    at Module._compile (internal/modules/cjs/loader.js:999:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1027:10)
    at Module.load (internal/modules/cjs/loader.js:863:32)
    at Function.Module._load (internal/modules/cjs/loader.js:708:14)
    at Module.require (internal/modules/cjs/loader.js:887:19)
    at require (internal/modules/cjs/helpers.js:74:18) {
  errno: -2,
  syscall: 'open',
  code: 'ENOENT',
  path: '/home/mike/node_modules/customerio-node/dist/package.json'
}