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`.
Fix rubocop issues within the Rakefile
[Resolver] Ensure Informative errors are always shown for platform incompatibilities

Closes https://github.com/CocoaPods/CocoaPods/issues/2868
[Bundle] Update Molinillo
[IntegrationSpecs] Update fixtures for Molinillo debug output going to STDOUT
Split linter messages from attribute names

Related to Core/#199. Makes linter messages more modular and informative
[Gemfile] Use Core from master
Merge pull request #2866 from CocoaPods/linter-attr-name

[Linter] Split linter messages from attribute names
Merge branch 'master' into swift

* master:
  [Gemfile] Use Core from master
  Split linter messages from attribute names
  [IntegrationSpecs] Update fixtures for Molinillo debug output going to STDOUT
  [Bundle] Update Molinillo
  [Resolver] Ensure Informative errors are always shown for platform incompatibilities
  Fix rubocop issues within the Rakefile
  [rake] Do not scare user when running `rake bootstrap`.
  [rake] Make more resilient against not having installed bundle.
  [spec] Disable tests that require mercurial to be installed if it's not.
  Revert "[Rake] Check required binaries"

Conflicts:
	spec/cocoapods-integration-specs