Track2: azcore log remove some duplicate code

[magodo]

The PR removes some duplicate code in azcore log.go:

• Remove the check on l.lst in Logger.Writef as it is checked in Logger.Should already
• Reuse Logger.Writef in Logger.Write to DRY.

• The purpose of this PR is explained in this or a referenced issue.
• The PR does not update generated files.
  • These files are managed by the codegen framework at Azure/autorest.go.
• Tests are included and/or updated for code changes.
• Updates to CHANGELOG.md are included.
• MIT license headers are included in each file.

[jhendrixMSFT]

The call to l.lst() in this case was intentional, to avoid interpreting any % characters as format specifiers (URL-encoded query params will contain them).

[magodo]

I've revert this.