remove compile-time find_library() checks for presence of shared library

If this package gets precompiled and cached before the user has
installed a pre-requisite shared library, then installing said library
will not fix the problem if the check for the presence happened at
compile time. Likewise, if PackageCompiler.jl is used to compile an app
on another machine, then absence of a required shared library at
compile time there cannot be rectified later by a user who downloaded
a pre-compiled app containing this package. Dropping the compile-time
check for the presence of the required shared libraries fixes this.
The exception raised by ccall() if the required library is missing is
anyway more informative than the warning messages removed here.

https://julialang.github.io/PackageCompiler.jl/dev/devdocs/relocatable_part_3/

src/WAV.jl

@@ -61,18 +61,9 @@ There is not a native backend for Windows yet.
 function wavplay end
 wavplay(fname) = wavplay(wavread(fname)[1:2]...)
 @static if Sys.islinux()
- @static if Libdl.find_library(["libpulse-simple", "libpulse-simple.so.0"]) != ""
- include("wavplay-pulse.jl")
- else
- wavplay(data, fs) = @warn "libpulse-simple not found, wavplay will not work"
- end
+ include("wavplay-pulse.jl")
 elseif Sys.isapple()
- @static if Libdl.find_library(["AudioToolbox"],
- ["/System/Library/Frameworks/AudioToolbox.framework/Versions/A"]) != ""
- include("wavplay-audioqueue.jl")
- else
- wavplay(data, fs) = @warn "AudioToolbox.framework not found, wavplay will not work"
- end
+ include("wavplay-audioqueue.jl")
 else
  wavplay(data, fs) = @warn "wavplay is not currently implemented on $(Sys.KERNEL)"
 end