Remove ECMA_STRING_CONTAINER_HEAP_NUMBER.

[zherczeg]

Does not provide a gain:

Benchmark	Perf (sec)
3d-cube.js	1.806 -> 1.792 : +0.796%
3d-raytrace.js	2.054 -> 2.004 : +2.451%
access-binary-trees.js	0.868 -> 0.861 : +0.737%
access-fannkuch.js	4.033 -> 3.925 : +2.668%
access-nbody.js	2.123 -> 2.084 : +1.841%
bitops-3bit-bits-in-byte.js	0.818 -> 0.821 : -0.328%
bitops-bits-in-byte.js	1.150 -> 1.135 : +1.296%
bitops-bitwise-and.js	1.899 -> 1.907 : -0.416%
bitops-nsieve-bits.js	2.872 -> 2.870 : +0.066%
controlflow-recursive.js	0.566 -> 0.563 : +0.545%
crypto-aes.js	2.013 -> 1.985 : +1.387%
crypto-md5.js	1.013 -> 0.995 : +1.699%
crypto-sha1.js	0.946 -> 0.928 : +1.891%
date-format-tofte.js	1.501 -> 1.487 : +0.975%
date-format-xparb.js	0.672 -> 0.654 : +2.717%
math-cordic.js	2.103 -> 2.066 : +1.760%
math-partial-sums.js	1.126 -> 1.108 : +1.570%
math-spectral-norm.js	0.980 -> 0.980 : +0.051%
string-base64.js	4.959 -> 4.921 : +0.772%
string-fasta.js	2.454 -> 2.436 : +0.762%
Geometric mean:	+1.166%

0.4K binary saving

[LaszloLango]

missing comment: /* !JERRY_NDEBUG */

[LaszloLango]

LGTM

[zherczeg]

Thanks, fixed

[dbatyai]

LGTM