[gdb/testsuite] Remove gcc/93866 xfail in methods.exp

The test-case gdb.go/methods.exp contains an xfail for PR gcc/93866.

However, that PR has been marked resolved-wontfix, with clarification that the
gccgo symbol names for methods are correct, even if they're not the same as
for gc.

Remove the xfail.

Tested on x86_64-linux with gccgo-10.

gdb/testsuite/ChangeLog:

2020-02-25  Tom de Vries  <tdevries@suse.de>

	PR go/18926
	* gdb.go/methods.exp: Remove gcc/93866 xfail.