backend: gl: do not leak back and default mask textures

[absolutelynothelix]

remove an unused function and fix two issues reported by leaktrace:

$ apitrace leaks picom.trace
33: error: texture 1 was not destroyed until 7003
40: error: texture 2 was not destroyed until 7003
$ apitrace dump --calls=20-49 picom.trace
// process.name = "/home/helix/Work/picom/build/src/picom"
20 glGenQueries(n = 2, ids = {1, 2})
21 glDisable(cap = GL_DEPTH_TEST)
22 glDepthMask(flag = GL_FALSE)
23 glEnable(cap = GL_BLEND)
24 glBlendFunc(sfactor = GL_ONE, dfactor = GL_ONE_MINUS_SRC_ALPHA)
25 glDisable(cap = GL_STENCIL_TEST)
26 glStencilMask(mask = 1)
27 glStencilFunc(func = GL_EQUAL, ref = 1, mask = 1)
28 glGetIntegerv(pname = GL_MAX_VIEWPORT_DIMS, params = {32768, 32768})
29 glViewport(x = 0, y = 0, width = 32768, height = 32768)
30 glClearColor(red = 0, green = 0, blue = 0, alpha = 1)
31 glClear(mask = GL_STENCIL_BUFFER_BIT | GL_COLOR_BUFFER_BIT)
32 glGenFramebuffers(n = 1, framebuffers = &1)
33 glGenTextures(n = 1, textures = &1)
34 glBindTexture(target = GL_TEXTURE_2D, texture = 1)
35 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MIN_FILTER, param = GL_LINEAR)
36 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MAG_FILTER, param = GL_LINEAR)
37 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_S, param = GL_CLAMP_TO_EDGE)
38 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_T, param = GL_CLAMP_TO_EDGE)
39 glBindTexture(target = GL_TEXTURE_2D, texture = 0)
40 glGenTextures(n = 1, textures = &2)
41 glBindTexture(target = GL_TEXTURE_2D, texture = 2)
42 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MIN_FILTER, param = GL_NEAREST)
43 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MAG_FILTER, param = GL_NEAREST)
44 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_S, param = GL_REPEAT)
45 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_T, param = GL_REPEAT)
46 glBindTexture(target = GL_TEXTURE_2D, texture = 0)
47 glBindTexture(target = GL_TEXTURE_2D, texture = 2)
48 glTexImage2D(target = GL_TEXTURE_2D, level = 0, internalformat = GL_RED, width = 1, height = 1, border = 0, format = GL_RED, type = GL_UNSIGNED_BYTE, pixels = blob(1))
49 glBindTexture(target = GL_TEXTURE_2D, texture = 0)

[codecov]

Codecov Report

Merging #1009 (8245de2) into next (5b6f6ec) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             next    #1009      +/-   ##
==========================================
+ Coverage   37.58%   37.59%   +0.01%     
==========================================
  Files          49       49              
  Lines       11155    11157       +2     
==========================================
+ Hits         4193     4195       +2     
  Misses       6962     6962              

Impacted Files	Coverage Δ
src/backend/gl/gl_common.h	30.23% <ø> (ø)
src/backend/gl/gl_common.c	25.40% <100.00%> (+0.18%)	⬆️

[absolutelynothelix]