test: drop test-run skipcond for gh-7762 test

Since luatest provides <skip_if> helper, .skipcond file is not necessary
anymore and is removed.

Needed for #8252

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

test/app-luatest/gh_7762_luajit_enable_checkhook.skipcond

-import platform
-
-# Disabled on FreeBSD due to #4819.
-if platform.system() == 'FreeBSD':
-    self.skip = 1
-
-# vim: set ft=python:

test/app-luatest/gh_7762_luajit_enable_checkhook_test.lua

@@ -2,6 +2,9 @@ local checktrace = require('jit.util').traceinfo
 local t = require('luatest')
 
 local g = t.group()
+g.before_each(function()
+    t.skip_if(jit.os == 'BSD', 'Disabled on *BSD due to #4819')
+end)
 
 -- Test payload to be recorded. It calculates the arithmetic sum
 -- of elements from 1 to the given n.