func (s *ProtectedBranchesService) UnprotectRepositoryBranches(pid interface{}, branch string, options ...OptionFunc) (*Response, error) {
	project, err := parseID(pid)
	if err != nil {
		return nil, err
	}
	u := fmt.Sprintf("projects/%s/protected_branches/%s", pathEscape(project), branch)
	req, err := s.client.NewRequest("DELETE", u, nil, options)
	if err != nil {
		return nil, err
	}
	return s.client.Do(req, nil)
}
UnprotectRepositoryBranches unprotects the given protected branch or wildcard
protected branch.

GitLab API docs:
https://docs.gitlab.com/ce/api/protected_branches.html#unprotect-repository-branches
package gitlab
import (
	"fmt"
)
type ProtectedBranchesService struct {
	client *Client
}
type BranchAccessDescription struct {
	AccessLevel            AccessLevelValue `json:"access_level"`
	AccessLevelDescription string           `json:"access_level_description"`
}
type ProtectedBranch struct {
	Name              string                     `json:"name"`
	PushAccessLevels  []*BranchAccessDescription `json:"push_access_levels"`
	MergeAccessLevels []*BranchAccessDescription `json:"merge_access_levels"`
}
type ListProtectedBranchesOptions ListOptions
func (s *ProtectedBranchesService) ListProtectedBranches(pid interface{}, opt *ListProtectedBranchesOptions, options ...OptionFunc) ([]*ProtectedBranch, *Response, error) {
	project, err := parseID(pid)
	if err != nil {
		return nil, nil, err
	}
	u := fmt.Sprintf("projects/%s/protected_branches", pathEscape(project))
	req, err := s.client.NewRequest("GET", u, opt, options)
	if err != nil {
		return nil, nil, err
	}
	var p []*ProtectedBranch
	resp, err := s.client.Do(req, &p)
	if err != nil {
		return nil, resp, err
	}
	return p, resp, err
}
func (s *ProtectedBranchesService) GetProtectedBranch(pid interface{}, branch string, options ...OptionFunc) (*ProtectedBranch, *Response, error) {
	project, err := parseID(pid)
	if err != nil {
		return nil, nil, err
	}
	u := fmt.Sprintf("projects/%s/protected_branches/%s", pathEscape(project), branch)
	req, err := s.client.NewRequest("GET", u, nil, options)
	if err != nil {
		return nil, nil, err
	}
	p := new(ProtectedBranch)
	resp, err := s.client.Do(req, p)
	if err != nil {
		return nil, resp, err
	}
	return p, resp, err
}
type ProtectRepositoryBranchesOptions struct {
	Name             *string           `url:"name,omitempty" json:"name,omitempty"`
	PushAccessLevel  *AccessLevelValue `url:"push_access_level,omitempty" json:"push_access_level,omitempty"`
	MergeAccessLevel *AccessLevelValue `url:"merge_access_level,omitempty" json:"merge_access_level,omitempty"`
}
func (s *ProtectedBranchesService) ProtectRepositoryBranches(pid interface{}, opt *ProtectRepositoryBranchesOptions, options ...OptionFunc) (*ProtectedBranch, *Response, error) {
	project, err := parseID(pid)
	if err != nil {
		return nil, nil, err
	}
	u := fmt.Sprintf("projects/%s/protected_branches", pathEscape(project))
	req, err := s.client.NewRequest("POST", u, opt, options)
	if err != nil {
		return nil, nil, err
	}
	p := new(ProtectedBranch)
	resp, err := s.client.Do(req, p)
	if err != nil {
		return nil, resp, err
	}
	return p, resp, err
}