Remove low RAM special casing for heap growth multiplier

Moved to change the default value in runtime.cc. This enables
changing the value by passing in a
-XX:ForegroundHeapGrowthMultiplier value.

This enables devices to set the foreground heap growth multiplier
to non 1.0 values even when low_memory_mode is true. Doing this
reduces GC frequency and can help device performance.

Increased the limit to 5.0 since the old limit of 1.0 was bogus.

Bug: 67416130
Test: test-art-host
Test: make and flash

Change-Id: I86166830261c034255c23611cb8f4ebcf8c43b09