Some small fixes for staticcheck

[RebeccaMahany]

Addresses some, but not all, occurrences of staticcheck violations in the following categories:

Code simplifications:

• S1000 - Use plain channel send or receive instead of single-case select
• S1005 - Drop unnecessary use of the blank identifier
• S1023 - Omit redundant control flow
• S1030 - Use bytes.Buffer.String or bytes.Buffer.Bytes
• S1038 - Unnecessarily complex way of printing formatted string
• S1039 - Unnecessary use of fmt.Sprint

Misuse of standard library:

• SA1016 - Trapping a signal that cannot be trapped
• SA1019 - Using a deprecated function, variable, constant or field

Dubious code constructs that have a high probability of being wrong:

• SA9004 - Only the first constant has an explicit type

Stylistic issues:

• ST1005 - Incorrectly formatted error string