string: Remove malloc attribute from para_realloc().

string: Remove malloc attribute from para_realloc().

Quoting from the corresponding section of the gcc-10 manual:

	This tells the compiler that a function is 'malloc'-like, i.e.,
	that the pointer P returned by the function cannot alias any other
	pointer valid when the function returns, and moreover no pointers to
	valid objects occur in any storage addressed by P.

	Using this attribute can improve optimization.	Compiler predicts
	that a function with the attribute returns non-null in most cases.
	Functions like 'malloc' and 'calloc' have this property because they
	return a pointer to uninitialized or zeroed-out storage. However,
	functions like 'realloc' do not have this property, as they can return
	a pointer to storage containing pointers.

Found by code inspection, the unpached code never caused problems.
Also, the function definition in string.c does not contain the
attribute.