Remove easyjson in preparation for switch to jsoniter

The jsoniter library does not require code generation, which is a
massive advantage over easyjson (it's also about the same in
performance). Begin moving over to it by removing the existing
easyjson code.

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

vendor/github.com/mailru/easyjson/jlexer/error.go

@@ -1,15 +0,0 @@
-package jlexer
-
-import "fmt"
-
-// LexerError implements the error interface and represents all possible errors that can be
-// generated during parsing the JSON data.
-type LexerError struct {
-	Reason string
-	Offset int
-	Data   string
-}
-
-func (l *LexerError) Error() string {
-	return fmt.Sprintf("parse error: %s near offset %d of '%s'", l.Reason, l.Offset, l.Data)
-}