Revert "[Rake] Check required binaries"

This reverts commit 581eb06a0aec59df0b0c5ab79113cfea970d0a62.

Conflicts:
	Rakefile
[spec] Disable tests that require mercurial to be installed if it's not.

You'll see output at the end of a run like:

```
[!] Skipping test due to missing `hg` executable: Installs a Pod with different subspecs activated across different targets

[!] Skipping test due to missing `hg` executable: Installs a Pod with an external source
```
[rake] Make more resilient against not having installed bundle.
[rake] Do not scare user when running `rake bootstrap`.