Remove alias of load to unsafe_load

[miry]

There are method Psych.load and alias load to unsafe_load exists in same time.

According the code load is now decorate safe_load.

Rdoc generates docs base on alias: https://docs.ruby-lang.org/en/3.1/Psych.html#method-c-load

The same versions exists in ruby https://github.com/ruby/ruby/blob/fb4df44d1670e9d25aef6b235a7281199a177edb/ext/psych/lib/psych.rb#L276

I assume the changes should first made here. Let me know if it is correct.

[hsbt]

@miry Good catch. Thanks.

@tenderlove this alias is needless after replacing safe_load by default. If you have any concern, Please ping me.