fix linter errors thrown by unconvert, goconst, and nakedret (#3960)

* Remove unnecessary type conversions

* Consolidate repeated strings into consts

* Clothe return statements

* Update blockchain/v1/reactor_fsm_test.go

Co-Authored-By: Anton Kaliaev <anton.kalyaev@gmail.com>

This PR repairs linter errors seen when running the following commands:
golangci-lint run --no-config --disable-all=true --enable=unconvert
golangci-lint run --no-config --disable-all=true --enable=goconst
golangci-lint run --no-config --disable-all=true --enable=nakedret

Contributes to #3262

crypto/multisig/bitarray/compact_bit_array_test.go

@@ -21,7 +21,7 @@ func randCompactBitArray(bits int) (*CompactBitArray, []byte) {
 		}
 	}
 	// Set remaining bits
-	for i := uint8(0); i < 8-uint8(bA.ExtraBitsStored); i++ {
+	for i := uint8(0); i < 8-bA.ExtraBitsStored; i++ {
 		bA.SetIndex(numBytes*8+int(i), src[numBytes-1]&(uint8(1)<<(8-i)) > 0)
 	}
 	return bA, src