fix: don't make plasmagun explosion on body

[WofWca]

This partially reverts f011fe9,
i.e. makes the plasmagun behave as in the original Quake III.

Also see the ioquake3 repo MRs:

• fix: don't make plasmagun explosion on body ioquake/ioq3#801.
• Revert "Bug 5066 - Plasmagun and BFG don't play the explosion when they hit players, patch by Ensiform" ioquake/ioq3#824.

The commit message of the reverted commit refers to
https://bugzilla.icculus.org/show_bug.cgi?id=5066 :

Plasmagun and BFG don't play the explosion when they hit players

Adds plasma and bfg to list of weapons that cause explosion
still on player hit.

The plasmagun and BFG explosion effect is not played
when hitting players, and if the distance traveled isn't very long
it can be kind of confusing if it even hit at all.

Patch to add plasma and bfg to list of weaps
that cause explosion + bleed.
I checked quakelive and it seems at somepoint
they changed it there too.

However, the plasmagun explosion on body (flesh) hit
makes quite a big difference gameplay-wise,
due to its visibility impact, you cannot see the player being hit
too well.

For reference, in Quake Live the plasmagun also doesn't make
its original explosion effect on body hit,
but BFG does.
So this commit also hopefully brings the behavior in line
with the intent of the Quake III authors.