Adapt GitTool.DescriptorImpl.doCheckHome for Jenkins 1.563

The doCheckHome method was declared to throw an exception, but this
implementation does not throw any exception.  Declaring that exception
breaks compilation with Jenkins 1.563.  Removing the exception throw
also seems to work with older Jenkins versions.
Merge commit '6eddb7e7b0a8e1d4d2ec98a05b0f2c171113cacc' into HEAD