remove `tls` override from mysql dsn normalizing (#468)

Fixes https://github.com/pressly/goose/issues/460

README.md

@@ -83,7 +83,7 @@ Options:
   -allow-missing
     	applies missing (out-of-order) migrations
   -certfile string
-    	file path to root CA's certificates in pem format (only support on mysql)
+    	file path to root CA's certificates in pem format (only supported on mysql)
   -dir string
     	directory with migration files (default ".")
   -h	print help
@@ -91,9 +91,9 @@ Options:
     	apply migration commands with no versioning, in file order, from directory pointed to
   -s	use sequential numbering for new migrations
   -ssl-cert string
-    	file path to SSL certificates in pem format (only support on mysql)
+    	file path to SSL certificates in pem format (only supported on mysql)
   -ssl-key string
-    	file path to SSL key in pem format (only support on mysql)
+    	file path to SSL key in pem format (only supported on mysql)
   -table string
     	migrations table name (default "goose_db_version")
   -v	enable verbose mode

cmd/goose/driver_mysql.go

@@ -9,7 +9,6 @@ import (
 	"fmt"
 	"log"
 	"os"
-	"regexp"
 
 	"github.com/go-sql-driver/mysql"
 	_ "github.com/ziutek/mymysql/godrv"
@@ -21,7 +20,7 @@ import (
 // type.
 func normalizeDBString(driver string, str string, certfile string, sslcert string, sslkey string) string {
 	if driver == "mysql" {
-		var isTLS = certfile != ""
+		isTLS := certfile != ""
 		if isTLS {
 			if err := registerTLSConfig(certfile, sslcert, sslkey); err != nil {
 				log.Fatalf("goose run: %v", err)
@@ -38,12 +37,7 @@ func normalizeDBString(driver string, str string, certfile string, sslcert strin
 
 const tlsConfigKey = "custom"
 
-var tlsReg = regexp.MustCompile(`(\?|&)tls=[^&]*(?:&|$)`)
-
 func normalizeMySQLDSN(dsn string, tls bool) (string, error) {
-	// If we are sharing a DSN in a different environment, it may contain a TLS
-	// setting key with a value name that is not "custom," so clear it.
-	dsn = tlsReg.ReplaceAllString(dsn, `$1`)
 	config, err := mysql.ParseDSN(dsn)
 	if err != nil {
 		return "", err