[Command] Don't check for git >= 1.7.5

Git 1.7.5 is no longer depended on due to
https://github.com/CocoaPods/Core/commit/99748b5b9fa8fe6541218f1752c0379589c7a6ee

Reverts 4ab76e807cb7bae409ee058d63dd6bfd3dac77ca
Merge pull request #2783 from CocoaPods/remove-git-1.7.5

[Command] Don't check for git >= 1.7.5