Removed redundant mentions to error codes in doc/api/errors.md
Fix this issue: "Every description of each error code starts with one of two unnecessarily-verbose phrases that should probably be removed:" https://github.com/nodejs/node/blob/master/doc/api/errors.md#nodejs-error-codes
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documentation is changed or added -
commit message follows [commit guidelines]
Affected core subsystem(s)
doc/api/errors.md