Enchantment type from item contains level of enchantment.
Parse give you error because you try making something like this:
add "sharpness 1 %level of sharpness 1 of itemtype%" parsed as an enchantment type to {_e::*}
if you wanna get level of enchantment use:
%enchantment level of loop-value%

Code (Text):

1. function removeEnch(i: item, e: enchantment):
2.     loop enchantments of {_i}:
3.         set {_ench} to "%loop-value%"
4.         add "%(length of {_ench}-2) first characters of {_ench}% %enchantment level of loop-value%" parsed as enchantment type to {_e::*}
5.     disenchant {_i}
6.     loop {_e::*}:
7.         if "%loop-value%" does not contain "%{_e}%":

Don't use 'add' with arrays, its so long, because on every 'add' you iterate list, make it like this:

Code (Text):

1. some loop:
2.   add 1 to {_i}
3.   set {_list::%{_i}%} to object

 

What version of skript are you using?
On 2.6.3 my code works fine, but if you have lower version I think you need put loop-value to variable before get level of enchantment, its old bug with parser, also with code like:

Code (Text):

1. loop 10 times:
2.   set {_list::%loop-value+1%} to loop-value

{_list::%loop-value+1%} except parse error, but in 2.6.3 this bug fixed anyway

In situations like this thread I prefer to use reflection code with Skript-reflect, its faster than spend some hours to solve problems with parser.

 

You dont answered about version of Skript?
If you need simply function to remove enchantments you can use:

Code (Text):

1. remove %enchantments% from enchantments of %itemtype%