Remove newline characters from ssh key before processing it.

Fixes issue https://github.com/gogits/gogs/issues/370

In short gogs stores ssh keys with newline characters (\n). When it wants to remove the key from `authorized_keys` it searches for the ssh key without the newline chars and thus fails to find and remove it.

Dev branch is currently broken, it compiles but gogs can't start due to template errors, so I can't directly confirm the patch for dev.
I tried the fix on the master branch and it works as it should.
Also I checked with the command you use to verify the ssh key (`ssh-keygen -l -f tpmPath`) and it let newline characters to pass, so at least I know that the problem exists on dev.
The problem is that newline characters don't have to be at the end of the key content in order to pass the ssh-keygen test.

For example a problematic entry was this (throw away key):
```
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDRirCAAPS+dNuhvMDA2FoAaOoQj54i2hD28YNiHk+tcAEUhlOkB0wmannTDBjpxSaIGeog4pUCj+IrZ7yuk3fARVvCIZ9ZzydEHyZb8YGh3GvmnNUU0EmEh8U4Hb4A2swB0mYmynU33vpyPFgfsNIDjZ2CYagTZsapVZTjyYG8iDDbIewDtMEFNuyTYnqqULzH4XVM3Q/g1njLhJqVXwGqw/djd9dawTQrmtYL14DzEQw5dcmG4iCJnD7CVXmns05XBElLjELeC0aS0dcaErvtS8GzPjA2Wefw+Obu14GRNk3NpNAq65QGck23olFY82qRRzwKfZ7f1p9ALx5Z3lhF 
andmarios@gentoo
```
The newline character is between the key and the _andmarios@gentoo_ string.