Scripting: don't call lua_gc() after Lua script run.
Scripting: don't call lua_gc() after Lua script run.

Calling lua_gc() after every script execution is too expensive, and
apparently does not make the execution smoother: the same peak latency
was measured before and after the commit.

This change accounts for scripts execution speedup in the order of 10%.

spearhead-ea/redis,ttuna/msot-redis,MSOpenTech/redis,splitice/redis,splitice/redis,MSOpenTech/redis,xuzhezhaozhao/redis_reading,darksideofthemoo/redis-histogram,Hailei/redis,louisliangjun/redis,maodeyi/redis_lua,louisliangjun/redis,darksideofthemoo/redis-histogram,ramonsnir/redis,HunanTV/redis,ttuna/msot-redis,HunanTV/redis,Hailei/redis,ksarch-saas/redis,spearhead-ea/redis,ttuna/msot-redis,HunanTV/redis,Hailei/redis,louisliangjun/redis,ksarch-saas/redis,spearhead-ea/redis,maodeyi/redis_lua,himoca/redis,HunanTV/redis,MSOpenTech/redis,xuzhezhaozhao/redis_reading,jxwr/redis,ramonsnir/redis,jxwr/redis,maodeyi/redis_lua,xuzhezhaozhao/redis_reading,MSOpenTech/redis,ramonsnir/redis,darksideofthemoo/redis-histogram,jxwr/redis,himoca/redis,splitice/redis,ksarch-saas/redis,splitice/redis,Hailei/redis,ttuna/msot-redis,ksarch-saas/redis,slfs007/mk-redis,MSOpenTech/redis,himoca/redis,louisliangjun/redis,slfs007/mk-redis,ttuna/msot-redis,xuzhezhaozhao/redis_reading,darksideofthemoo/redis-histogram,slfs007/mk-redis