Fixed misspellings reported at [Bug #16437], only in ruby and rubyspec.

I noticed that some files in rubygems were executable, and I could think
of no reason why they should be.

In general, I think ruby files should never have the executable bit set
unless they include a shebang, so I run the following command over the
whole repo:

```bash
find . -name '*.rb' -type f -executable -exec bash -c 'grep -L "^#!" $1 || chmod -x $1' _ {} \;
```

Previously, trying to use this would result in:

undefined method `uri' for #<DRb::HTTP0::ServerSide:0x00000aec9f1637f8> (NoMethodError)

Also, use a relative require to load sample/drb/http0.rb.

Fixes [Bug #13431]

* Drop duplicated sample code

* Drop another style sample

https://github.com/ruby/ruby/pull/2389#issuecomment-522489520

* Update sample list

```
sample/observ.rb:30: warning: assigned but unused variable - clock
```

Kernel#inspect does not call #to_s now

To follow https://github.com/ruby/ruby/commit/fd7dc23d281f38a71fa7f9c32812cd468c4b1788

* Standardize to load date libary code

> git grep 'require .date.' | wc -l
179
> git grep 'require .date\.rb' | wc -l
1

* Simplify