Remove omit.js

[ehmicky]

Fixes #1048

This removes the omit.js dependency. Besides not being well maintained, it includes an old version of core-js which prints warning messages on npm install.

We do not want to use lodash.omit because it is huge (1500 lines of code compared to 12 lines of code for omit.js). This is because lodash.omit comes with all the extraneous features and utility helpers of the whole Lodash ecosystem. Tiny modules are much simpler to debug and less bug-prone.

I could not find any well maintained alternatives on npm except for filter-obj, which we already use. However it needs to be wrapped with a tiny utility function to make it more convenient.

[codecov]

Codecov Report

Merging #1050 into master will increase coverage by 0.23%.
The diff coverage is 100.00%.

Impacted Files	Coverage Δ
packages/build/src/error/serialize.js	100.00% <100.00%> (ø)
packages/build/src/plugins/env.js	100.00% <100.00%> (ø)
packages/build/src/utils/omit.js	100.00% <100.00%> (ø)
packages/config/src/utils/omit.js	100.00% <100.00%> (ø)
packages/cache-utils/src/hash.js	89.04% <0.00%> (+2.73%)	⬆️
packages/build/src/install/main.js	97.77% <0.00%> (+4.44%)	⬆️

Flag	Coverage Δ
#macOS	96.72% <100.00%> (+0.29%)	⬆️
#node_13	97.55% <100.00%> (+0.01%)	⬆️
#node_8_3_0	96.55% <100.00%> (?)
#ubuntu	97.66% <100.00%> (+0.12%)	⬆️

[oles]

You're on a roll, @ehmicky.
I had no idea lodash.omit (and most likely the others in similar format) were so bloated.
That's concerning, and a shame.