Removed alpha keyword from unit data. Change image files to have it

data/units/Dark_Spirit.cfg

@@ -12,7 +12,6 @@ alignment=chaotic
 advanceto=null
 cost=54
 usage=scout
-alpha=0.7
 unit_description="Dark Spirits are messengers and bearers of tidings from the realm of the dead, and a force of dread in this world. Happily, they have rarely been seen in Wesnoth."
 get_hit_sound=groan.wav
 	[attack]

data/units/Ghost.cfg

@@ -12,7 +12,6 @@ alignment=chaotic
 advanceto=Wraith,Shadow
 cost=20
 usage=scout
-alpha=0.5
 unit_description="Ghosts are the souls of warriors that died in agony centuries ago without leaving a corpse behind. Not limited by physical bodies, these undead can fly swiftly towards their victims."
 get_hit_sound=groan.wav
 	[attack]

data/units/Nightgaunt.cfg

@@ -12,8 +12,6 @@ alignment=chaotic
 advanceto=null
 cost=50
 usage=scout
-alpha=0.75
-skill=nightstalk
 unit_description="Nightgaunts haunt the night, keeping their ugly faces behind masks in an effort to hide their souls of pure evil. These despicable creatures are able to hide at night, leaving no trace of their presence."
 get_hit_sound=groan.wav
 	[attack]

data/units/Shadow.cfg

@@ -12,7 +12,6 @@ alignment=chaotic
 advanceto=Nightgaunt
 cost=30
 usage=scout
-alpha=0.75
 skill=nightstalk
 unit_description="Souls blackened by evil, Shadows roam the night attacking unsuspecting foes. These incorporeal fiends are able to hide at night, leaving no trace of their presence."
 get_hit_sound=groan.wav

data/units/Spectre.cfg

@@ -12,7 +12,6 @@ alignment=chaotic
 advanceto=null
 cost=44
 usage=scout
-alpha=0.75
 unit_description="Spectres, the most powerful ghosts in the undead ranks, can use their powers to summon a spectral sword that drains the life out of their foes to strengthen themselves. They also have a terrible wail that freezes the heart of the weak."
 get_hit_sound=groan.wav
 	[attack]

data/units/Wraith.cfg

@@ -12,7 +12,6 @@ alignment=chaotic
 advanceto=Spectre
 cost=34
 usage=scout
-alpha=0.5
 unit_description="Wraiths are some of the most powerful ghosts in the undead ranks. They can summon a spectral sword that drains the life out of their foes, thereby strengthening themselves. They also have a terrible wail that freezes the heart of the weak."
 get_hit_sound=groan.wav
 	[attack]